"When someone writes "fuck all police" they're stereotyping and that's wrong."

Not exactly. To stereotype, someone would have to be expressing a fixed idea about what all police are like, such as "all police are racist. Fuck them." This would be stereotyping. When someone says "fuck all police," if they are at all intelligent, they are most likely expressing their hatred for what police must do as part of their job, i.e. their role in society as defenders of the interests of private property, their role in enforcing the law, etc. They may be expressing their hatred for people who are willing to carry out this job. To say "I hate police because of what they do in accordance with their role in society" is not to stereotype. Sorry, but you are wrong.