I agree, we wouldn't have to worry about food poisoning if all people who prepared food would, oh, let's say, WASH THEIR HANDS after going to the toilet. I work in a college of Pharmacy, and you wouldn't believe how many professors barely rinse their hands. It's disgusting. end rant But there will always be people who prepare food with abysmal hygiene. Antibiotics were originally used as a protection against instances like this.
Should antibiotics be added to food in the quantities they are now? Nope. But they do serve a (limited) purpose. We need to protect our food supply from bacterial contamination (and careless people who get others sick), and so far, antibiotics have been one of the only ways to accomplish this goal. Now, though, radiation sterilization may hopefully make antibiotics obsolete in food preparation.
But if you're worried about antibiotics in your meat, slow-cook it - most antibiotics are heat-labile, which means they're broken down when exposed to heat for any significant period. The ones we use in the lab for tissue culture experiments, penicillin and streptomycin, are inactivated if they're above room temperature too long.
Short version of a long-winded post: Better to have tiny amounts of antibiotics in your system than salmonella! :ick:
(sorry, that was probably way more geekage than anybody wanted! I'd better shut up now, before I wax semi-elegant on overprescription of antibiotics and antibiotic-resistant bacteria!)