Can't you see the difference between fear that person A will do something legal, protesting/strike action (but not liked by the group in question) & fear that person B will do something illegal, abusing a position of power via racism or working with vulnerable people (also not liked by the group in question) are very different stances?.
The fact you seen to think union membership (potential to do something legal) is in some way comparable to BNP membership or high risk individuals (potential to do something illegal) high-lights a degree of bias of your own.
Did you not earlier advocate that these are things you could find out on employing them and dismiss them if they are breaking the rules? Does this advice only apply to some cases? Either we are judging people by their behaviour or we are not.
I really don't see how your position holds any form of consistency in this thread.