If we're comparing the situation to average joes, let's say I made a mistake and broke some rules that caused someone to miss a week of work (we'll leave violence out of the question, since it's obviously not acceptable in most normal situations.) I would probably lose my job, I would be lucky to get off with a fine. It's impossible to really compare apples to apples, but my point is that the NFL wants to change the culture and make these kind of hits unacceptable, and fines are one of the few semi-effective methods they have available. (Now, if they really cared about player safety, they would bring the regular refs back in, but that's another conversation.)