I used to be very opinionated about firearms. Regarding DA/SA, I agreed that is was an answer to a question nobody asked and that it made no sense to have 2 different trigger pulls. Real "gun pros" all know that the 1911, or at least SAO, is the best option.
Flash forward to '05 when my first trip to a combat zone, I'm issued a P226 and an AK47
. So much for opinions...now they don't mean squat 'cause I'm headed outside the wire on RTE Irish with 2 guns I wouldn't have picked ('cause they're stupid) and I haven't even so much as had a chance to test-fire them!
No option forced me to learn how to run each platform to its full potential (with the help of professional instruction, an accessory or 2 on the AK and lots of practice.)
Now, I just see guns as tools. Each one and each different action type will have a set of strengths and weaknesses. Keep the strengths, address the weaknesses through a combination of training, technique, and in some cases accessories and mods (like a replacement or RDS for the AKs crappy sights).
My carry guns are DA/SA now (P6 and 226). Advantage for high stress combat is that the DA pull offers extra margin of safety while also being devoid of an external safety lever to operate. Another advantage is the nice SA pull for all shots after #1 and the short reset. Bonus points for thumb control of hammer on re-holster. Disadvantages have been covered already.
Of course, if you are able to pick and buy/carry what you want, get what you like and shoot well. That is a nice option to have. I did 2 Army tours with an M9 after that 1st contractor stint...I don't like M9s much either.
(I shoot them very well though
)