Yanbu to expect that comments shouldn't be made, as nobody really knows what someone is going through.
You've had lots of replies along the lines of 'don't be rude if someone's off wirh stress', but I get the impression from your OP that you wouldn't think it appropriate to say these things to the people involved, and that even if you suspect someone is taking the mick or could manage to work, it'd be out of order to say otherwise.
All those studiously defending the rights of those off for weeks for stress, should be at least as thoughtful about your time off., as they're not qualified to judge your ability to work when ill.
Although an unpopular opinion, GPs do seem to be quick to offer to sign people off work for a couple of weeks at a time to help 'stress', when there are lots of other options to support different elements of ill mental health.
I presented to my doctor with headaches, extreme anxiety and lack of energy, and due to questioning about high workload, I was offered some time signed off. I didn't take it, as the element of having the bare minimum of my work covered and having to pick up excess when back would have made me more anxious! Turns out my diet was able to relieve lots of the symptoms and talking therapy helped me to deal with underlying issues.
Wtongly or ightly, now if I have a mental health wobble on occasion. I actually tell my employer its a cold/flu/bug for a couple of days!