Bicycle Mechanics - Pulling a Bike Trailer: Bad for Bike?

I just spent and arm and a leg replacing bottom bracket, chain, chain ring, etc on my mountain bike. Most likely due to all the hard woods riding. A (road) racing friend saw me pulling my two children in a bike trailer and said it was very bad for the bike. I didn't bother then to ask why, but now I'm curious. Is this in any way, shape or form harming any part of my bike?

one of my co-workers rides an old S-works titanium/carbon MTB for work and he also pulls his 2 year old boy in a burley bee trailer around all the time (he, of course, has electrical tape and old inner tube wraped where the trailer connects to the frame). so far, he hasn't had any problems, and he's had that frame for a few years, and has probably been towing the kid since he was 1. the trailer is pretty much always attached to the bike. i think i've only ever seen him without the trailer once.

he also rides a giant, yellow cargo trike, and can kick my ass up on road rides...

I have an ancient Peugeot Uo-10 I use specifically for hauling big loads; most of the time it hauls a trailer. Use it 2-3 times a week. I've noticed no damage to the frame of the bike.

Only damage it can make is a little scratch where the attachement sits on the frame, no big deal..
I would probably not use an expensive road bike to pull a trailer but a mountain or trail bike of any kind should handle it, otherwise it's not even made for rough terrain and probably not safe.. (my $0.02).

I've towed my two kids in my Burley D'Lite for about 5 years and have not had any problems with my old Raleigh Technium Pro.

Pulling a trailer will certainly put more load on the drivetrain, rear spokes, and brakes. Depending on the weight distribution it will put additional load on the frame at the attachment point. A BOB trailer will also put some additional twisiting force on the rear triangle. It shuld be obvious that these additional loads will cause greater wear and tear on the components. However, it's not like the bike is in danger of total or irrepairable failure.

There are plenty of people who tow trailers on cross country tours. Enjoy taking your kids for rides. Hopefully you will spark a lifelong interest in cycling. I'd say that's worth a few extra component replacements.

I pull a BOB cargo trailer every day. It hauls varous junk, probably about 25lbs of stuff that I trolly around between work home and errands. I pull it behind a early '90s Giant Excursion touring bike--it's a triple ring so I have plenty of low gears. I have not experienced any failures that I can attribute to anything other than the age of the bike, however I would imagine that drive train components are wearing out a bit more quickly due to the extra load but I think that's minimal.