I'm aware you don't want a debate on what you can and can't do re masks. None of this is aimed at you - but it's why there's animosity.
Part of the issue is that masks are so hugely important in preventing the spread, we all have a duty to try if at all possible. And the problem is that lots of people just can't be arsed to try because it is either inconvenient or takes a bit of getting used to.
There is a very long list of conditions which could make you potentially exempt. A fair number of people who are technically exempt could wear a mask if they wanted to, but it's just less hassle not to bother and point to the exemption instead.
Their mask protects me. If their mask protected them, I suspect there's a lot of people who currently don't wear a mask who might start wearing one. This country is full of selfish fuckers. Asian countries have been wearing masks for years without any of these issues.
I'm not suggesting for a second OP that you are being lazy or that you could wear a mask. If you can't, you can't. There are absolutely people who really can't wear a mask who are genuine. But all the genuine folk are being affected by people who just can't be arsed, or who don't believe they should have to, so use a technicality to get out of it.
And for the record, I could be exempt too. I persisted and wear a mask because we are all supposed to be in this together. Again OP, not suggesting you're able to do this - but there are many people who could who simply don't.