The thing about concrit is that some people react very badly to it. And concrit I've received so far wasn't actually constructive. For example, a person told me once, "I really didn't like it when Draco did this and this and now I can't finish the story." I'm not sure what I'm supposed to say to that. "Okay!"? Betas are a wonderful source of concrit. *nods* (
Yes, bashing (in this sense) is a fandom term. It's a combination of bad characterization and excessive character hate. Just as Mary Sues are a combination of bad characterization and excessive character love.