From what I've noticed, most of the problems come more from the people who give the tasks rather than Amazon itself. For example, some people might bribe you to vote for their dog/cat/cousin on some website. That one is just a minor ethical issue, but I also noticed a few tasks that wanted me to go to poorly-rated websites or try and advertise for a Multi-Level Marketing scheme.
Reporting such things might be a problem as there is no drop-down list as to why a task is being reported. It just gets reported and that's it.