People are going to have disagreements, because they're going to have different opinions. Nothing wrong with that. Everyone has the right to voice their opinions, but they aren't guaranteed their opinions will go unchallenged. The problem is when challenging crosses over into personal attacks and abuse.
I did that once, in the first six months of this blog, when I went to Devon Sanders' old blog and basically told him he didn't understand Cassandra Cain's character and he should shut up until he did. Which was out of line, and thankfully, he didn't tolerate it. He deleted the comment, and told me I wasn't welcome any longer, which was the smack upside the head I needed. That wasn't the person I wanted to be, so I sent him an apology, which he accepted (he didn't have to, but he did), and since then, I think I've avoided personal attacks on other bloggers. I still disagree with other people a lot, but I try to stick to addressing the problems I have with their opinions.
It took me a little longer to extend the same courtesy to comic creators. Probably because I had it in my head they were getting paid at least in part by me, so I could throw out all sorts of insults here. Which is stupid. Also, I'm sure I thought it was cool and edgy to talk about wanting to hit Chuck Austen with a pipe wrench for the sin of writing bad X-Men comics. Which is also stupid. And I still think they were bad comics, just like I think Civil War was a disjointed mess of moments that were meant to look cool, but didn't really make any sense, especially when viewed in the larger context on the shared universe they were taking place in. But it's one thing to say that, and another to go, "Augh, Mark Millar sucks and he should die!" I don't think I said that specifically, but I'm sure something along those lines was typed at some point.
Disliking something or a person's body of work is fine, and talking about the whys can be a productive exercise. And heck, if you met the someone and they were an ass, then sure, say so. The problem with me was, I don't know any of those people I was talking shit about, and so it seems foolish for me to be getting personal about it. I doubt any of the professionals ever noticed me, I'm one voice in a wall of voices screaming either praise or invective. But it's still embarrassing to look back on some of the stuff I said in the past, because there just wasn't any need for it. So I'm sorry for all the out of line things I said in the past, and I'm trying my best to make sure I don't repeat those mistakes now or in the future.