It's obviously bad in the NHS, but it goes much further than that. I remember my FIL telling me about the large company where he worked - going back decades now - where the union boss would actually come around and demand to know why people hadn't taken all of their sick leave 'entitlement', and ordered them to 'be off sick' for a week or so of his choice.
It was indeed seen as part of their annual leave entitlement - and not taking it was cosying up to the management (the enemy) and not supporting their colleagues who either did need the paid sick time or, I'm guessing more likely, didn't but took it anyway, and making them look bad.
They would also insist that, if the 'main' worker (electrician, engineer or similar) was off sick or on holiday, his 'mate' (assistant) couldn't possibly come in either and do any other separate jobs (organising, admin, planning or whatever) independently - so it was already a 2-for-1.
Unions have done so much essential good for us all; but there is always the danger that some people will royally take advantage - and undermine the purpose for (and the retention of) all of our so hard-won vital rights.
Because of widespread abuse of workplace sick pay policies, we're already in a situation now, across the board, whereby the default assumption when somebody calls in sick is that they are lying. It makes things doubly hard for people who do genuinely have serious recurring health problems and are written off as serial advantage-takers.
People will hark back to 'the old days' when, if you didn't turn up for work, you didn't get paid. They will cite far fewer people being off sick in those times as 'proof' that loads of people nowadays are swinging the lead; when in reality, back then, a great many people who really shouldn't have been at work would go in anyway, because they simply could not afford to lose the pay.