The poor reputation of unions in the US is well-deserved. The unions are writing their own anti-union propaganda, you can't blame other people for noticing this. Your argument is essentially that we should pretend this obvious badness doesn't exist because it makes unions look bad.

It is weird how much discourse these days is about pretending something obviously true isn't actually happening. The first step of fixing a problem is being honest about its existence. The inability of some people to be honest about the existence of obvious things is why so many problems go unaddressed.