I think the point is that some of us find the entire idea of "mandatory gratuity" insulting. While I've never worked a food/drink service job, I have friends who do and I generally tip well.

It's just annoying to have the hotel or restaurant dictate how much I *must* tip, even if I receive bad service. I'm in complete agreement with FlyByMike in that a server probably ends up missing out on tip by forcing me to pay a fixed percentage.