In order to answer this, I'd need to compare the efficacy of both the for-profit and the non-profit organizations. In some countries you don't get paid, and I don't know if that leads to blood shortages.

I side with you. I've donated over a gallon of blood and blood products throughout the years. You're helping someone. The reason they pay you is to incentivize coming and doing it. It's painful for the donor, and it takes a while for your body to recover. The company doing so is (in my experience, anyway) a non-profit organization. They exist to help people. They do make money, but that's because they have to pay their employees and donors, as you've mentioned.

I'm usually sitting or lying down.

Tissue, cell and organ donation (including blood, semen and oocytes) can and should be done strictly not-for-profit. This is how it's done in Spain (well, you do get a snack when donating blood and a small amount of money for oocytes since the process is quite long) and there's usually no shortage of blood components in hospitals. Local governments do a lot of campaigning, set up mobile units etc., which seems to work; people see all of that, think of it when planning their day, and many even go in small groups to donate.

If it’s an adult doing the selling, then it’s a consensual interaction.

Exploitation in the negative sense requires a violation of consent.

How could selling something you naturally produce be a scam? I can see how easily you could get ripped off on the price, but in the end you're still making money and automatically replacing the plasma lost. Even if they're not actually using the plasma for their stated purpose, I'd still argue the donator is not the one getting scammed. I guess it really comes down to your definition of "scam".

I've donated blood and plasma and each time I've been offered rewards but don't bother claiming them. I do it to help others. My job pays me enough to live on.

I think it's fine to pay some for it.

I don't know how your healthcare system is structured. But let's assume there is a profit motive in getting you to donate blood. Let's also assume profit is a problem. So we want to reduce profits.

1. If you get €25 per donation that is €25 less profit for them per donation.

2. The demand for blood is going to stay the same. No one will decline a live saving surgery because it's a bit expensive and will pay anything to get it. Increasing supply will decrease profit margins.

Maybe it should be like other charitable donations and there should be a set tax deduction per ml or better yet how about they take enough for donation and decanter a portion out an do blood testing both to make sure the blood is clean but alsoso the individual is aware of they are free of X. You could get like a qr code you can use to identify the results later.