I think it's fair to say that different people find different phrases offensive, and when you encounter language that you find offensive, you should let people know. However, I don't think it's right to scold people for their language- as I said earlier, I think it's better to say "I find that offensive, that offends me" instead of "That's offensive, don't say that kind of thing." There's no one word that is universally offensive to everyone, but I'm sure that every word offends at least once person. Letting someone know that you, personally, are offended, lets them know that when they are around you, they need to watch what they say. It also helps to open their eyes to the fact that the way they talk can be hurtful to others.
I'm going to guess that the backlash the OP received was the result of basic herd mentality to return perceived hostility with more hostility and defensive behavior. We're they right? No. Is it understandable? From a psychological standpoint, yeah. Best way to avoid that kind of thing in the future is to let them know they've offended you, not that they've offended everyone.