This isn't even about the fine bros. I don't think it ever really was.
This is about Youtube as whole. People are angry at youtube, and the fine bros just happened to be caught doing the way wrong thing at the worst time possible.
Let's look at what has happened on Youtube lately. IHE's channel (and other channels) have been removed. Nostalgia Critic recently came out with the news that his videos lost monetization with no explanation of why, and he asked Youtube to clarify this occurrence for 3 whole weeks without any word in response. And, to top things off, smaller fish in the youtube sea - who might have otherwise stayed silent - have since piped up about how they've been screwed by Youtube's shady handling of flagging, copyright, etc.
Abuses of these systems are nothing new, but tensions around this issue have come to a boil within the past week or so.
Only amplifying the anger is the fact that you can't fight Youtube. They have a monopoly on online video services, so no matter how many IHE or Nostalgia Critic-sized channels make a stink about these shady polices, the company really has no reason to do anything. They have nothing to lose.
It is in this sort of environment that the Fine Bros, with seemingly no amount of savvy or awareness of these tensions, have basically announced that they have found innovative and world-changing ways to abuse Youtube's copyright system. And now, as a result, we have the easiest target in the world. It takes about 2 seconds to dislike, unsubscribe, and hurt the Fine Bros channel - protesting Youtube's practices by proxy - and no one can do shit to stop this. There aren't even any loyal fans who might sway opinion or rally a defense. Literally no one will save the Fine Bros from an angry mob that has just been waiting for something tangible to fight.
Yes, things are slowing down now. However, I suspect that IHE and other medium-to-large channels will start uploading responses to and analyses of this situation within the next few days, which will only raise awareness and incite more anger. And god help them if a huge youtuber like Pewdiepie says something.
Either way, this is just the beginning. So grab the popcorn.
TL;DR Youtube has been fucking things up for awhile, and no one can stop that, so the Fine Bros and their abuse of Youtube's system have become the target of people's rage instead.