I agree. Fiddling with the selector in the middle of a firefight is a bad idea. But looking for a fresh mag to stuff in your weapon is worse.
In a firefight, your rifle should be on semi-auto. You should be taking aimed, rapid-fire shots.
3-round burst means one shot is aimed, 2 are not. Your 30 round magazine is empty with 10 pulls of the trigger on 10 targets.
Which is worse -- thumbing the safety to full-auto when you need to empty the last 20 rounds at the guy rushing your position, or fumbling for a new magazine because you don't have 20 rounds left in your mag?
By the way, one of my favorite combat rifles in the Steyr AUG. There is no selector. When you want to take aimed, semi-auto shots, you squeeze the trigger. When you want to empty the magazine, you PULL BACK HARD ON THE TRIGGER. Very natural.