Not liking Constructive Criticism shows that you think your work is perfect, which nearly never the case. Unless you're the next Michelangelo or Donatello, there's always going to be something you can improve upon, especially with MOCing. That doesn't mean you can't be satisfied with your work, but in order to improve, you have to accept that your work is flawed in some way.
The issue becomes when "good" artists refuse to take criticism because they think they're perfect. Since they have made things that people praised in the past, they see themselves as above those who are are giving the critique.
For example, I know one MOCist who was pretty good. I won't give his name, but let's just say he's a former member of this community. He posted a MOC once, and there was a lot of legitimate critique about it. However, since the MOCist viewed himself as "pretty good," he refused to listen to the advice of others, especially those who hadn't posted MOCs publicly. Thus, the MOC didn't improve, and the MOCist didn't improve either.
I don't post real MOCs often anymore, and I know that I'm not very good. However, I KNOW that I was worse before @Hawkflight came along to criticize my MOCs. While it kinda hurt at the time, it absolutely helped me develop my skills. I think Rockho said it best,
So do I think critiquing a MOC is hostile or rude? No, not at all. In fact the opposite.
I think people sometimes get confused though, and think that "critique" applies to comments like "this moc sux". That's not critique, that's a statement of opinion, and one not supported by any evidence. Honestly, it shouldn't even be lumped in with the rest of critiques.
In sum, Constructive Criticism is...constructive, and the sooner you accept that, the sooner you can grow, even if you think you are perfect.