Awww Give yourself and your species some credit! We may not all be saints but people are good, becoming a brony has showed me just how MANY people are good and willing to believe in virtues beyond themselves but still desire inner happiness. Earth isn't all bad either and it's only getting better as medicine advances, freedom of information is spreading, human rights have improved. I've been all over the world, every nation I've been to has been blessed with such nice and welcoming people. I've seen the bad too though. But hey! Equestria isn't perfect either. Remember how the three tribes almost doomed themselves because of how much they hated each other? What about the Buffalo and the settlers of Appleloosa? Even in the idyllic Ponyville, the townsfolk were xenophobic to Zecora at first. You take the good with the bad. I don't think humans would taint Equestria, and I assume the portal turns you into the local's shape anyway. If your a good person, Equestria would have a home for you, simple as that.
I know right? Geez I thought we were supposed to be the idealistic and hopeful internet subculture. (Sorry for the short reply.)
Actually. Now that you mention it. According to the Book of Revelations, after the battle of Armageddon where evil is defeated, God will rule his Kingdom on Earth and all will be good. Celestia's reign over Equestria just might resemble what that will look like!