There are parts of Mexico that are not safe for locals or tourists. The same could be said for other parts of the world. There are also people that just don’t know how to travel safely and do dumb things when traveling.
TA is a business, and to make money they need business on their side, and for that they need to suppress certain types of critical feedback. The same applies to Yelp, Amazon, and other review oriented sites..
I've always hated this part of TA's rules. They prohibit any discussion of violence or criminal activity. WHY? If you were knocked down and robbed at gunpoint in the parking lot of a hotel I'm considering I think that's relevant information.