The hate was because it replaced function keys many people use by tactile touch, without looking. Doing the same on a touch screen is very difficult.
If the bar had been added on top of those, I don't think there would've been the same kind of hate for it.
Even without tactile elements it was two keys to use function keys.
I would have been fine with the touchbar if it just default displayed function keys. Hitting fn+f5 to quicksave is annoying.
I didn't really mind the fn keys being there. I rarely use function keys unless I'm RDP'd to a Windows machine.
What drove me crazy though was the escape key. They later added the physical escape key back but I think at that point it was a bit too late.