I'm noticing a trend of mothers with small children who bike alone. It's too bad we all don't live closer to each other as then we would have someone to trade childcare with and someone to bike with! That being said I bike alone all the time, my partner worries about me more than I worry. I am prepared and carry tools, snacks, H2O, cell phone, a warmer layer. I bike wherever I feel like biking, we have a beautiful network of trails half a mile behind our house. The upside is even if I end up on a new trail (which is always super-technical) I can head down and return home. Our trails also tend to be busy so I (foolheartedly?) assume that I would be found within a reasonable amount of time. On that note I am more worried about bears and mountain lions than scary men. Odds are, around here, you will be attacked by a bear first.
In my humble opinion fear is a crappy reason not to do something.
"I think it has done more to emancipate women than anything else in the world. It gives women a feeling of freedom and self-reliance. I stand and rejoice every time I see a woman ride by on a wheel...the picture of free, untrammeled womanhood." Susan B Anthony