If you live in a country where you have to pay for basic healthcare, and you have an option to be paid for a blood donation you would have done anyway, then by all means take them dollars. The issue is that people who shouldn’t be donating - either because it will put them in danger (e.g. they are already too weak), or because it will put the recipient in danger (e.g. because they have some serious infection) will now be encouraged to donate. This is why pretty much every other country bans payments for blood donation.