It's a little unnerving, but it's not as bad as it seems on the face of it.
The trigger still has to be pulled in order to fire the gun, and the grip safety has to be depressed before the trigger can be pulled.
The thumb safety only blocks the sear. It doesn't lock or block the hammer.
If the sear were to suddenly disintegrate, the hammer would fall, and it would wipe the safety off faster than you can do it with your thumb...and the odds of that happening are about as good as winning the powerball three times in a row.
If the hammer hooks were to fail, the sear would grab the half cock and stop the hammer.
If the sear crown cracked, the sear would still grab the half cock and stop the hammer.
And if it happens to be equipped with a Series 80 or Swartz system...the firing pin is blocked unless the trigger is pulled or the grip safety depressed...respectively.
So, breathe easy and keep your finger off the trigger until you want the gun to fire.