I have the same story in the same country with presumably the same organization (Sanquin). I used to give blood, but not anymore because I don't find what they're doing ethical.
Both of the key claims do seem to have evidence to support them:
1) Paying for blood shifts the socioeconomic distribution of the donor pool.
2) The socioeconomic shift results in more contaminated blood due to greater incidence of drug use and/or related blood-borne diseases that cannot all be tested for with high accuracy.