I would give a big fat 'NO'.
To my mind a flag should only be applied when someone is posting outright illegal subject matter. It should not be about one's opinion of what constitutes a valuable post. There are individuals on here that I would never upvote because I do not personally enjoy what they produce. There are even times I find what they do to be offensive. But I also know that my opinion is not flawless and I should not rule the world or steem with it.
I was remarking to a friend from another social media site today, that steemit does not suffer from trolls the same way his said platform does. That is because the flag is effective, the way it is. Changing flags to downvotes would probably encourage people to use it. They would see it as an opportunity to express their opinions and that is is, in my opinion, what the comment section is for. The flag button should only be used in extreme situations. We should be encouraging people to support other bloggers and not downvote those we disagree with or even worse are jealous of because they have received a large payout.
Now that steemit is a monetized platform through ads. We want to encourage the folks on here to come back and come back often. You do not want them chased off by downvotes.
Generally speaking, a blogger receives upvotes because of two reasons. They have paid for promotional bots, which must maintain steem power to be of any use, or they have networked and produced in a sustained and positive manner. Either way, they are supporting the ecosystem that is steem and neither way should they be punished for it.
Nice commentary.