What is the relevant difference between unpaid whole blood donation and paid plasma donation?
I would argue that the price of blood is inflated due to low supply. Increasing the supply by paying blood donors could very well reduce the unit price of blood, and thus patient costs.
I reject your insinuation that paying people for donating blood poses a threat to the blood supply. The risks to human life posed by an insufficient blood supply are far greater than the risks arising from compensating donors.