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."

the potential harm associated with "nitrates" has been addressed by someone else, and with MSG specifically, some people simply have unpleasant reactions to it (though these results are difficult to reproduce clinically, they are listed at http://www.mayoclinic.org/monosodium-glutamate/expert-answer..., the desire to avoid the risk of these effects is quite rational) and there's additionally no reason a non-essential compound such as MSG needs to be used - using artificially-isolated compounds to modify one's neurologic reaction to food is a practice that a lot of us choose not to participate in, and we'd prefer the food is of enough quality to start with that such modification is not necessary in order for it to taste good. There is no "fear" that MSG is causing actual harm, only that it's a sign of an otherwise low-quality food product. Hence we appreciate when a product marks it as not included.