This one is extremely easy to figure out.
One is accepting someone's desire to be something, the other is accepting someone's desire to not accept someone being something. It takes very little thought to understand why a culture of acceptance would be okay with the first and not the second. Being okay with the second is inviting the culture of acceptance to be destroyed by unaccepting people.
Really, the entire thread concept comes down to holding too closely to the exact definition of acceptance and applying it universally, which will inevitably create a paradox. The OP is basically built on a stupid word game.