we can have a flagging system without a reputation system!
making it transparent for everyone if a post or comment is "undesireable" in any way by others and by whom!
but without that person actually being hindered in his further blogging from having recieved f.x. 50 downvotes / flags on his recent post!

Generally, as we can just comment our thoughts and feelings, we can use that to convey anything that we otherwise use the flagging to convey..
For instance just a comment where you write "Flagging this!" or a jpg or gif with a flag or thumbs down !
like this