Society changes slowly, but someone must start that change. If a person wants to, let them walk around in a rainbow dash costume with MLP tshirt and a plushie. It doesn't matter as long as no one is getting hurt. Though, I have heard that some areas are particularly intolerant, to the point of threats.
And as for me, I have MLP backgrounds on my computer and a 'squee' ringtone but other than that, i havent really had much opportunity to go out in public with MLP merchandise, as I really only recently got into the fandom and have yet to fully tackle the familial aspects of it.