I live in an area with lots of cyclists, but it is a bit "countryfied" at points. I never worry about my safety. Sure bad things happen everywhere, but i really don't think about it. If i felt my safety was compromised, i wouldn't ride in that place. My husband never tells me where i should or shouldn't ride. He asks, of course, but I never go anyplace that would be considered dangerous. I do avoid a few what i consider to be dangerous or really scary traffic situations, which my husband doesn't care about (he is a fearless rider).
I don't, however, mountain bike alone, with one exception. There's a trail by my house that's about 5 miles round trip, with other little extensions. It's not too challenging so i will do an out and back mtb ride there. I figure if there's a problem, I can walk back to my car. I went once at another place, that has a lot of trails and i felt creepy being there alone, even though I have been there several times with my husband. Plus, I got lost and was freaked out. So, do whatever your comfort level dictates.