I completely agree with what you are saying here and actually wrote a post about the spammers on Steemit a few days ago.
I reply to people who plagiarise content or leave spam messages on my posts all the time. And I have no issue flagging their posts as well. There's nothing worse than people clogging up Steemit with stolen material or spammy content, it makes it harder for the good content to shine through in addition to making Steemit appear like a platform with nothing but shit posts.
Yeah it's really good to flag them, because they are not letting us grow and show our best, they are ruining it to all of us, no education, no morals, no intelligence they have, I think that such people have to be blocked, no body need them or their accounts.