That implies intent and from a teleology philosophical argument, the "flag" means it should be for abuse only
Let's put aside the issue of "downvote" vs. "flag" for the moment. Even though I don't entirely agree with your statements, in part because I don't always use the steemit.com interface, I will grant that flagging implies abuse. The point is still that abuse is subjective and excessive upvoting (including but not limited to by the poster himself and another close associate whale) can very well be a form of abuse.
Historically, the reason for the change to the icon was to discourage downvoting just because you don't like a post. For example, if someone posts a song, some people like it, the reward is not excessive, but you happen not to like it, the intent is to discourage you from frivolously downvoting.
This is very different from downvoting based on seeing excessive rewards as a form of abuse. Let me be clear: I happen to like this post and found it interesting. I didn't flag/downvote it based on like/dislike (if given a like/dislike button that didn't affect rewards, I would click like), but based on my subjective view that excessively rewarding these posts constitutes a form of abuse.
@lukestokes
I can't speak for others but 100% of the time I post a comment when I downvote for any reason (and sometimes to state a reason when upvoting if I have a reason worth noting other than "I like it and want to see it rewarded"). Obviously we can't force everyone to do that, but I definitely encourage it.
Reading through the various posts I've seen here regarding etiquette, it's hard for me to put aside the "downvote" vs. "flag" issue because, to me, it's the crux of the confusion as more and more people describe what the flag is for (preventing abuse). I get that a minority of people use other interfaces for the Steem blockchain, but I think it's safe to argue most use Steemit.com which does make a distinction between a downvote and a flag.
I guess, for me, it's hard to agree with all abuse being subjective (I'm coming from Sam Harris' Moral Landscape perspective), because some things the community, as a strong majority, does come to agreement on, such as frivolously downvoting being a detrimental activity for the network.
I agree with you, excessive upvoting can be seen as a form of abuse, especially by the very small minority which currently have such a huge influence over total payouts. Currently the interface provides no simple mechanism for: "I like the post, but feel the payout is excessive, so I'm going to vote against it using my own influence to bring the payout down, thus leaving more payouts for others." If the flag had a "reason" option which included some text (it could even just auto-post a comment to that effect if we didn't want to change the blockchain structure for the new meta data about the flag), then I think it would solve so much confusion here. It would even still follow the "abuse prevention" intent a flag implies.