Can someone explain the Will discourse to me?

I will start by saying that I haven't seen Season 5 yet, I'm waiting for the whole thing to come out. I actually tried my best to avoid all spoilers, but it's downright impossible at this stage.

So, having said all that, I have to ask: Why are people so upset by Will coming out as gay? Wasn't it obvious back in Season 3 already? Are people upset because he's gay and they didn't see it coming or is the moment itself badly executed? I genuinely want to know.