NO, the blood transfusion people are not saying that the blood of gay people is unclean....they take lesbian blood for a start.
What they are saying is that the likelihood of them being infected with HIV is higher than the average, as it is for other specific groups all of which are excluded from donating.
There may be a lag between getting (and being infectious) and showing up as positive of three months.
Given that the blood transfusion people actually gave people HIV in the 1980s they don't want to do it again.
You seem to b prepared to accept the increased risk of spreading the disease, they are not.
The costs of screening the blood of gay people isn't just measure in pounds, it is measure in infected people. And as yet no-one has come up with data to show that the blood transfusion people are so short of blood that the extra risk is worth taking
When I traveled in Africa I took a sterile kit, so that I didn't risk getting HIV from non sterile equipment if I had an accident, didn't that make me racist? No, it made me prudent.
If a risk anaylsis is carried out, and the relative risks are the same, or the difference not significant it would be time for a change of policy, but to want to do it simply to 'make people feel better about themselves' isn't rational.
Better to spend the time and effort on education