DAO has no use for a decocker and SA only should not be carried hammer
down on a loaded chamber in the first place. We have to be talking
about DA/SA.
With modern single action, should be able to carry hammer down on a loaded
chamber. The trigger lifts a striker in to position between the hammer and
firing pin has been required for at least 20 years. So a dropped firearm
would not discharge.
Even the old 3 screw Ruger Blackhawks can be refitted by the factory for free to have the striker (transfer bar) to make it safe to carry fully loaded.. However, reportedly it devalues the pistol and ruins its otherwise outstanding trigger. None of my 3 screws have the "upgrade". They are range queens and see no carry duty.