[aeternum]

Does it just not feel ethical or is one of their claims false?

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.

[amadeuspagel]

The second claim would applies just as much to the US.