Years ago I was attempting to create a CD rack (bored) using an old 3/4" piece of oak. I was going to dado some exact width slots in it for the CD's to stand up and tilt in, using a table mounted router.
After about the third or fourth dado slot I found the router bit came right up through the top (backside) of the piece. The router depth locking screw came loose (or I forgot to tighten it) and the vibration from the table made the router gear rack screw itself right up through the 3/4" depth of the wood instead on holding a 3/8" depth slot. I never figured that was possible until I was staring at the 30K RPM bit by my fingers.
Wasted piece of wood (made it shorter) but the lesson was a good one learned. Nobody got hurt but I never (If I ever did?) put my hands over top of the router bit, anymore, no matter how thick the piece is. Pusher sticks and distance became paramount.
For the first year or so I fussed under my breath, any time I had to run the table saw with the guard in place. Slowly, I began to realize that they really were not all that bad, in nearly all cases.
Now, I seldom think a second thought about the guards. The obvious exception is when using a tenion jig, or dado blade or other or other cuts that do not go all the way through the workpiece. Even then, there are guards available for the second class of cuts mentioned above.
So really, if everyone just made up their mind to keep with a guard until they got used to it, you would find that it is a rare case where the guard slows them down or prevents accurate cutting.