Foxes, like all wild animals, are opportunists. Whatever will give them the best results from the least amount of energy expended is what they'll go for. I've seen the results of a 15 pound fox taking out a 20+ pound wild turkey (turkeys don't go down without a fight), and I know people who have had cats taken by foxes.

Personally, I like them. We have them here in the middle of the city of Portland (Maine). The one in my neighborhood trots down the street about 3 AM on Wednesdays (rubbish day), looking fat and glossy and generally quite pleased with himself. We also don't have a large rodent problem having the fox around. That's definitely a plus in my book.