Indeed.
However, there are two problems, which won't be solved by changing the name from "flag" to "downvote":
The fear of retaliation (so only a few people dare to flag at all - these ones often actually really like doing it). I see no reason why this would change?
The abuse of the flag option when users with much SP follow every post and comment of their unlucky "victims" to flag them whatever they write.
Indeed.
However, there are two problems, which won't be solved by changing the name from "flag" to "downvote":