I don't know much about where/how the phrase "love and tolerance" originated, other than that it came from 4chan. But, in my opinion, it doesn't matter where it came from.
From watching the show, I know that it's about love and tolerance. I'm pretty sure someone else said in the replies about blind love and tolerance, and actually what they are referring to would undermine what love and tolerance truly is. Firstly, there is a difference between toleration and agreement. For example, I tolerate the practice of sadomasochism, because if responsible adults want to do it in a consensual, safe manner with each other, then it's not my place to judge them. However, I don't like or agree with the practice of sadomasochism.
Also, "love" is a general term, and doesn't mean that loving others requires not standing up for yourself, or not telling people when they're doing something harmful, etc. It means that you accept people for who they are, that you try not to judge people. That you try to understand others and put yourself in their shoes instead of instantly judging them. That you give people the benefit of the doubt and that you put other's wants and needs (depending what they are) before your own. However, this doesn't mean don't stand up for yourself, this doesn't mean let people take advantage of you. Just as Fluttershy learned in Putting Your Hoof Down, all it takes to stand up for yourself in verbal situations is a simple "no." Or, even simply ignoring the person. A lot of conflict can be avoided by simply saying no or walking away instead of getting into an argument, which can lead to a physical fight. In a physical fight, we all have the right to defend ourselves from harm. Unity is also a very core aspect of love. All of this is a part of love. Love for others, love for the world, love for ourselves.
In practically every episode there is a positive inspirational message about how to live in the world with love in your heart. If we all lived by the lessons in MLP, the world would be a much brighter, happier, more peaceful place. If people decided to accept other people for who they were, to put aside differences, to tolerate people you don't like or disagree with, giving people a second chance, to stand up for yourself by simply saying "no" or walking away instead of starting a fight, to put other people before yourself, the world would truly be a better place. All of these messages and more are found in MLP, some of them are more obvious than others. I will provide examples of things from the show representing what I wrote about in this paragraph.
Accept other people for who they are, to put aside differences: The very fact of the mane 6's friendship. They all have different personalities, yet they all accept and like each other for who they are, as they are best friends. A specific example of this would be how Rarity and Applejack learned in Look Before You Sleep that they could be friends even though their personalities seemed to be polar opposites.
To tolerate people you don't like or disagree with, giving people a second chance: Princess Celestia and Fluttershy wanting to reform Discord in the episode Keep Calm and Flutter On despite all the harm he had done to Equestria in the past is an example of toleration, and of giving people a second chance. There are some situations where certain behavior cannot be tolerated, such as crime, and sometimes you could give someone any number of chances and they wouldn't change. However, this rule doesn't apply to everyone. There have probably been at least one, if not more situations in all of our lives where we could have tolerated someone, or we could have given someone a second chance, but we chose not to. Intolerance can be one of the biggest fuels of hatred, and hatred can lead to war.
To stand up for yourself by simply saying "no" or walking away instead of starting a fight: Fluttershy learned this lesson in the episode Putting Your Hoof Down. There are two extremes: one, letting other people take advantage of you, and two, bullying and harassing others to ensure your own security. Both of these things are bad. Fluttershy learned how to find the balance between those two extremes: stand up for yourself without being hateful. How exactly this is done depends on the situation. You could just say "no," or just walk away, or otherwise say something that would fit the situation, without being hateful. If someone takes advantage of you, being hateful in response only leads to more conflict and hurt feelings. Standing up for yourself without being hateful greatly increases the chances of a peaceful resolution being brought to the situation, including you being separated from the negative situation without bullying or violence ensuing.
To defend yourself or others from physical harm: Though Equestria is a peaceful world with love and light (as depicted throughout the entire show, and referenced directly by Princess Celestia in The Crystal Empire, Part 1), that does not mean that they do not defend themselves from harm. When Princess Luna allowed her negative emotions to turn herself into Nightmare Moon and threaten Equestria with eternal night, the mane 6 united and used the elements of harmony to free her from the prison she had built for herself. When Discord attempted to turn Ponyville into the chaos capital of the world, the mane 6 united and used the elements of harmony to turn him back into stone, to prevent him from harming others. When Queen Chrysalis and her army of changelings attempted to enslave the inhabitants of Equestria and feed on their love, Princess Cadence and Shining Armor united and, with their love, repelled the forces of darkness. When King Sombra attempted to enslave all of Equestria and utterly destroy all light, love, peace, and happiness, the crystal ponies, with the help of Princess Cadence, Prince Shining Armor, and the mane 6, united and, with their love and light, destroyed King Sombra for good, extinguished his black magic, and reflected love and light throughout all of Equestria. The common theme here is that the inhabitants of Equestria choose to use their power to defend themselves from harm, instead of using their power to harm others. Princess Celestia knows black magic, as we learned in The Crystal Empire, Part 1. She could choose to use it to destroy everyone. But, she chose love and light, which lead to a prosperous, joyful, and peaceful Equestria. If, in our world, we learn to use violence for defense, and defense alone, we could put ourselves on the path to becoming a world of love, light, and peace.
Unity: Unity is a very common theme in the show, and is a very core aspect of love. If we all learned how to unite with one another instead of argue and fight one another, the world would become a much better place. We are all in this together. Any strife, conflict, and violence is the result of free will used for evil instead of for good. Our world is not doomed to be engulfed in perpetual darkness. What the world is like is each and every one of our choices made by everyone. We must live the change we wish to see. Unity is seen throughout the entire series as a general concept of peace and goodwill, a spirit to overcome conflict and differences toward a common betterment of themselves and the world. More direct examples of unity are The Cutie Mark Chronicles episode where the mane 6 learned they were all connected before they even met each other, whenever the mane 6 unite to use the elements of harmony, Princess Cadence and Shining Armor uniting in their love to drive away evil, and the entire population of the Crystal Empire choosing to unite, to grow the light and love within themselves, and, as one, drive away the forces of evil that threatened their lives.
This is not an all-inclusive list of spiritual, moral messages in My Little Pony: Friendship is Magic. True love and toleration (not sarcastic internet memes) should be of paramount virtue in each and everyone's heart, whether or not they are bronies.