I think paying for blood or other bodily fluids is bad. It provides incentive for desperate people (addicts etc.) to lie on the safety forms to keep getting paid.
I know a few people who donate blood despite not getting anything in return. I personally stopped donating plasma after a few times for health reasons (nothing dangerous in the plasma itself, luckily). To me, being able to help a hospital or a person by simply sitting back and watching shows on my tablet is probably the easiest, laziest charity you can support. The snacks are nice, too.
Not everyone can donate blood, but everyone who is able to, you should consider it, even if you won’t get paid for it. You can doom scroll and browse Lemmy like normal, except you’re sitting in a weird chair and get free food.
I suppose in the shittier countries, where all blood donation stuff is run for-profit, you should let them pay you if they’re making a profit off of you, but I still think it brings a bad incentive.