The thing is, even if you can wfh, not every company or manager is cool with you taking that privilege on random days that aren't scheduled as wfh.
Just randomly taking the whole week at home because ill, is exactly what I want to do when I'm ill. I'm not of the power through mind at all and I honestly don't want to go anywhere if not well.
However, we are sometimes forced into that mindset by others. In my experience it is genuinely frowned upon to call in sick for a cold, or anything that isn't keeping you completely tied to your bed.
I catch colds quite regularly, and when I've worked from home because of it, people gossip, perhaps because they are jealous I can do that and they can't (not everyone is allowed wfh in my office), nevertheless everyone talks behind your back as if you're taking the piss and that does affect you mentally and makes you paranoid and worried about it.
Management sometimes also makes it sounds like they don't really believe you; that you're not really ill unless you sound like Joe Cocker on the phone.
So you feel a pressure to come in as much as you can, even if that means taking your germs with you, and only stay at home when you really really can't leave your bed.
It's damned if you do damned if you don't.
I think it's ridiculous there is a stigma on taking sick days, but there just is. I also think that if managers can't tell a good employee from a bad one without looking at their sick days, they are a crap managers in my opinion, and encouraging ppl to come in ill. But unfortunately this is the world we live in.