Wikipedia say:

Social stigma is the extreme disapproval of (or discontent with) a person on socially characteristic grounds that are perceived, and serve to distinguish them, from other members of a society. Stigma may then be affixed to such a person, by the greater society, who differs from their cultural norms.

Most of us here are victims of a social stigma. Greater society has formed us all according to their preconceptions of manliness, femininity and adulthood. These preconceptions change over time.

Originally it was blue, not pink, that represented girls. Blue represented peace, serenity and kindness. Pink, as a tone of red represented the blood stained upon a warrior's clothes. No joke.

And ponies were gender neutral too. And purple was the colour of royals.

So, what happened? Where did our social stigma's come from? Why do they exist?

I'm not entirely sure why they exist, but they do, and they're a pain! The only one which ever made sense was the "Male must be strong/Female must be sensitive" stigma. This is because the woman is more invested in her child, having had to carry it and birth it before the man had a chance to bond with his child, whilst the man provided for his currently preoccupied mate. Nowadays, this doesn't make as much sense. We have (almost) equal rights, and fathers are encouraged to bond with their children. A saying has emerged.

"The only difference between genders is the equipment used in creating a child."

But we still have these stigmas, we still work more often in our gender-roles than in the opposite. Why must we do so?

Simple. It's programmed into us from when we are born. If we go against it, we will be rediculed and rejected. We will be unable to pass on our genetic data, a primal neccesity rooted in instinct.

So, why do we not hide this part of us? The part we know will be ridiculed?

Because MLP shows us that it's okay to be ourselves, it's okay to have a sensitive side. Because it's also telling little girls that very same message. It's okay to be smart, brash, shy, fabulous, country or crazy. You don't have to act dumb.

It is this very same message being rooted in our brains as we watch, and is the reason why we're not ashamed anymore.

But these social stigmas still exist. They've been rooted in the minds of everyone around us, and those around us hide these things, because they don't think it's right, even though it makes them feel happy.

Bronies aren't changing the definition of manliness. They're shattering social stigmas. They're changing how we view ourselves and those around us! But it wasn't just us bronies. It was Lauren Faust and her fantastic crew, those who created the show. They planted the seed, and we let it grow. Together, we shall finally break free of our binding chains. We shall be amazing.

TL;DR

Social Stigmas are awful. MLP isn't redefining manliness, but removing social stigmas in our minds. Yay MLP!