Hi jeffrey
I disagree.

I feed my fish lots and lots of live blackworms and they thrive on them.

I feed them tubifex too, when my lfs is out of blackworms and I've never had any problem.
I prefer to feed the live ones because I know they are clean and healthy looking. If they don't look good at the lfs, I won't buy them.

I don't like the frozen ones because they often smell bad and when they defrost, the blood runs out of the worms, which means good nutrition is being lost. Besides, I have no idea whether the frozen ones were alive or dead and rotting when they were frozen.
As far as bacteria goes, that is on all worms. If you live in the UK, they have a product called Myxazin that can be used to sterilize them before serving. Just rinse in a solution mixed at the rate of 2 drops per gallon for a few minutes.