We donate plasma for free here in the states, too. I’ve done it many times. It takes longer than donating whole blood, which is what deters many donors. Giving plasma is no more painful than giving whole blood (or any blood fraction.)
I don’t think there is anything wrong with selling plasma, and there are sites which pay for it. I guess my only quibble is that if you are taking money in exchange for it, you are selling, not donating, the plasma. I think its the same difference as donating a car as opposed to selling a car.
I was going to say something to that extent also. My initial reaction was, 1, if there’s money being received, it’s not a donation, it’s a sale; 2, I didn’t know that was done. I have never heard of donors receiving money (and I do donate blood), and when I first read the OP I had no idea how donating had anything to do with needing extra money. Some donor services (the ones I know in NY and NJ) give donors “points” and those can be redeemed for stuff, sometimes blood drives give away stuff, from t-shirts to gift cards, and of course there are the complementary cookies and juice.
As far as whether it’s ethical, I would look at it like this: If you would donate whole blood or plasma or platelets or whatever else, regardless of the reward (or usefulness thereof or lack thereof) then there’s no reason not to, even if the reward happens to be flat-out money. And there is also the fact that regardless of whether or not you as a donor are rewarded, the plasma would help people. I would just make sure that the organization is legit and all that. Like I said, I have never heard of getting money for donating blood or any of its parts (that doesn’t mean it’s untrue or wrong, I’ve just never heard of it. Now I have).
ETA: Again, as far as whether it’s ethical, would donating ever be unethical, even if there was a reward involved and that was the reason for the donation? (I’m not saying this applies to the OP, just posing the question.) There may be circumstances that would amount to a less than honorable motive behind a donation, but I don’t think a donation could inherently be unethical, because the recipient of the donation will benefit, provided that that which was donated is distributed fairly and justly, i.e., not being sold to those in need as a prohibitively expensive price.