just cause they provide the service free of charge doesnt mean they cannot abuse users. an brown townogy: server hosts can kick and ban anyone they want, but just cause they own/created the server doesnt make their actions justifiable or right, it just means they /can/ do that.
but in youtube's case, they /have/ to do it. their direct source of income is refusing to pay them for viewership on certain videos. if youtube were to continue to monetize said videos, the entire system would become unsustainable. youtube would be paying content creators out of their own revenue which would eventually result in a net loss. the only way youtube would be able to sustain themselves is if they payed everyone a smaller cut per view and in that scenario every channel on youtube would suffer
its easier to demonetize a video on why rape is ok than it is to pay an educational history channel video half as much per view. the former is better for business as well on all ends and is good in the public's eyes