For me it is just as fast to thumb back the hammer as it is to find the safety.
Is your manual of arms for 1911, safety off, hammer down, round chambered?
Rifleman55 & Acesn8's are right about how fast things can happen. This becomes glaringly apparent if you look at how thugs rob/assault people, at arms length. If you need to insert your pistol into a problem, chances are that you will need to do so robustly, because you are behind the power curve and using one hand, because you need your other hand to fend off an assault. So, any carry condition that A) compromises the establishment of a robust grip on the pistol and/or B) requires both hands to make the gun live can be seriously lacking in the context of self defense. You need to know how much time, accuracy, robustness, etc... you are giving up for different carry methods. A few ways to find out are to test it, on a timer, a qualifying course of fire and against a resisting partner.