As a retired U.S. Coast Guardman, I recommend fellows purchase a boat 18' or bigger. The winds often times come up on all our Souther California Lakes. You generally need a biger boat with at least a 150 hp engine to push you against the wind. I am not even sure that many of the Lakes you speak of will allow the boat you have purchased on the water. On the other hand, on a calm day, you could get away with a 12' boat.
I too believe it is dangerous. Years ago, at Lake Silverwood, I pulled in one of those 14' rentals with husband and wife. The wind had blown them againt the rocks and their small engine did not have enough power to get them off the rocks. Remember this, not all fishermen will come to your rescue should you get in trouble. Some will, some won't. So, what you want to do is not put yourself in possible danger by going on the water with a boat that is not rated to push you against the wind. Also, remember, that should you get into trouble on a lake, the fellow coming to your rescue must evaluate whether he can safely assist you. Oftentimes, the other boater, is not prepared to throw you a line and tow you to the dock. Always think safety when boating. YOUR SAFETY!
Hope this helps.
Lightlinejohn