Let me be blunt, costing charities time and money that they could use for their actual mission of helping people to find a life-saving match with a donor is a real shitty move. This is freeloading at its finest.
The OP commented in a different thread around the same time as your rant:
> "I should probably say that my primary reason for signing up to a stem cell donor registry is to actually be a donor! This data is generated as a byproduct of signing up and is also quite interesting on a personal level.
I was thinking that framing it in a way to also find out interesting things about yourself might be a good way to encourage people who might not have thought about it to sign up for the first time, and this would be far more cost-effective than a traditional in-person donor recruitment drive, but let me know what you think!"