[anthonyb]

Nitrates aren't harmful in themselves - it's the Nitrosamines that they can produce under certain conditions, which are very definitely carcinogenic.

Probably not so bad these days, since there have been steps taken to reduce the amount of nitrosamine in all sorts of foodstuffs. There's a good overview at http://lpi.oregonstate.edu/f-w00/nitrosamine.html

Given most of the information there, it's possibly a good reason to avoid the hippie celery juice bacon (though I've never seen it in the stores), mainly because you don't know how much nitrate you're getting. But it's a little more complex than "Lol, hippies."