Because the term means real things that can be legally fought against. If you misuse the term and teach others to misuse it, it's is more likely that other people will react incorrectly to challenges faced.
An easy way to undermine a movement is to look at people who are saying factually incorrect things to make their point and say "see? They don't know what they're talking about. Don't listen to them". And boom you've now made it easier to convince anyone on the fence to side against you.
It's a really easy and common divide and conquer strategy.
If you want to help people while firing them up, then feed them the real information about union busting and how companies are actually doing it.