Is it dumb or stupid to open the breech and check to see if a round is in the chamber? Of course it is. You should always have an absolute understanding of the condition of your gun and should know without question whether it is loaded or not and what it is loaded with. The reality of the situation is that humans are quite fallible and don't keep up with many types of information.
At Thunder Ranch, the teach doing "systems checks" that are a combination of first opening the slide to see if a round is in the chamber. If it is dark, you can do a feel by hand. After verifying a round in the chamber, then check the status of the magazine by dropping it into your had. You can visually inspect it and by feel tell if it is full or not. The folks at TR suggest checking the system twice a day, first when your day starts and when your day ends. You check at the beginning of the day so that you know things are ready for whatever comes up and you recheck at night because during the course of the day, you may have done something to your gun that caused harm. If you have ever been in a police station and seen all the marks on the door frames. you know that guns suffer a certain amount of abuse. Aside from checking to see if the gun is loaded, the systems check gives a quick feel to see that the parts do actually still move.
Why do this? While it may seem rather dumb to need to check to see if your gun is loaded, there have been a bunch of incidents of cops getting into gunfights with unloaded guns, and I am sure this has happened with civilians as well. Maybe there is a mag in the gun, but no round in the chamber. The place to find out your gun is not loaded is not during shooting.
A sign at a local PD's gun range on the road out of the range says "Stop and Load Your Weapons." It is a subtle reminder because apparently over the years, many of the officers have come in, done their qualifying shoots, presented their firearms for inspection, holstered and left without reloading. The armorer tells me that several officers have managed to start their qualifying shoots with unloaded guns, apparently as a result of having unloaded them sometime previously, say for cleaning, and then never reloaded. Some of the guys get by with several weeks of walking around with unloaded weapons!
If you come home tonight and see that your front door is open and you decide to sweep your own house, don't you think it would be wise to take a moment while you had it and do a quick check to see if your gun is loaded and mag topped off? That is the perfect time to do it.
On 1911s and maybe some other semi-autos without FLGRs, you can do the hooked thumb in the trigger guard press check. I personally do not think it is a good idea because it means that your index and maybe middle finger are right next to the muzzle, that you have inserted a finger within the trigger guard that is not a finger used to pull the trigger, and on a 1911, the gun has to have the safety off to do this. Somebody tugs on your shoulder to get your attention or accidently bumps into you while doing this and the potential is there for you to release the slide and the thumb to bump the trigger, discharging the gun in an uncontrolled, unaimed manner.