Your finger is the best safety. I have carried the Shield with no safety and the new Sig does not have one either. I carry with one in the pipe always. To me, in a defensive situation, the less things you need to think about when protecting yourself with a firearm the better. More safeties are equivalent to the gun control some states use when traveling with a firearm. For example, when a gun has to be stored in a locked box and separate from the ammo. If you are getting robbed or car jacked this will be no help as the perp is not going to wait while you get your shit together.
I guess if you are comparing hammer fired to striker fired then a safety is necessary. I think a grip safety would be sufficient in most cases. If the hammer cannot be released unless the grip safety is off then why have a secondary safety? I am sure issues of safeties can be debated all day long. It ultimately comes down to one's own comfort and abilities.
I agree with pretty much everything you said here. I don't carry a 1911 anymore, but when I did it was condition 1 and I still didn't like the idea of having to get the safety off before getting a shot off, even though it would instinctively be off by the time you've drawn. It's still a variable and seemingly unnecessary step. The Sig is DA only, with no safety and I carry a P30 in winter clothes and when I'm not working, it has a manual safety, but is DA/SA, so I carry it with the manual safety off and it's no different than carrying the Sig. I am not a fan of manual safety and I'm not a fan of strikers, so my options are fairly limited. I tried to learn to like the strikers, now
@ArtVandelay has my M&P. I just don't dig it.
You can find plenty of instances if you look where the perp got the first shot off before the the good guy gets his safety off. I know training is the ultimate solution, but still, why not remove as many variables as possible and keep it simple?