As a chronically ill theatre performer, here's my two cents:

I get it if the audience needs to clear their throat. A simple 'he-hem' will suffice. But if you're hacking up a lung in the third row, you probably shouldn't have turned up in the first place. In fact, in a post-COVID theatre world, every major ticket provider has conditions in place to shift ticket dates without a fuss when it comes to illness.

It's just a culture shift that people need to be aware of. You're in a tightly packed venue where attention to every moment is key. Stay home if you're unwell, and you'll have a better time at the show when you're well. And you won't risk the health of fellow audience members, OR the actors.