They’re engaging in blatant market manipulation. I’d say that harms people outside their group.
2008 produced a lot of resentment of the heads-I-win, tails-you-lose financial arrangement (in terms of financial services companies) of the Western world, but there wasn't any attainable way of actually taking action based on that belief.
Now, there is. WSB gets to have its lulz, specifically at the expense of those they feel wronged them (banks, traders, etc).
As the saying went in Eve Online from Goonswarm, it doesn't matter if you lose 1,000 ships, if everyone wants to hang out with you instead of the other team. Cultural victory.
I imagine the first HFT firms felt very similarly.