I am working on submitting a paper to the Proceedings of the National Academy of Sciences. They ask that I suggest editors and reviewers who are qualified to evaluate my paper. They also give me the option of listing a few people who I want to not be given the chance to peer review my paper. I assume this is so that if two authors have written on the same topic, and clashed on that topic, one can't keep the other from publishing by writing very negative reviews. It is a way to ask that your paper not be sent to your rival and then treated unfairly.
There are people whose previous conclusions I disagree with, but nobody I can think of who I have any reason to believe would treat my paper unfairly. I haven't been in the field long enough or published enough papers to make enemies yet. Something to look forward to, I guess.