As with everything, you must weigh benefits against risks. The fact is there are a great many women all over the world backpacking alone. Of course many join up with other women backpackers some time during their journey. Everyone knows there's safety in numbers, and it's fun to share experiences. Nevertheless, any lone backpacker will spend time alone, so she should know how to defend herself.
Some countries are more threatening than others.
Most women travelers love Italy and get along well. Morocco, on the other hand, is three hundred years behind Italy. Women traveling in developing countries must understand western status does not make them immune to the sexual time-warp. Indeed, in some countries the woman traveler is a prized sexual target for local men. This usually means nothing more than an uninvited man sitting at your table and asking pointed questions while you're trying to eat.