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.

If they see it as a scam then they seem to expect certain financial gain from donating. In my opinion this is bad as donating life-saving goods should not be done just for the money.

You can't be scammed if you are doing it for saving lifes (except if they sell the blood to some shady labs instead hospitals).

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.

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

Exploitation in the negative sense requires a violation of consent.