I think everyone's just trying to do their job and make sure the product is good.
Testing is a very vital part of every product. An engineer's job is to write code. The tester's job is to find bugs. The PM's job is to assign a priority to those bugs and the engineer will get to it based on the priority. It's just business.
I see no reason why engineers and testers can't have a beer together at the end of a day's work.