>Like it was a "safety hazard" to have too many people at once in the smoking area behind the textile mill. It is a slippery slope to try to tease apart what is, and what isn't, interference right?

No. It is a necessary thing to do and what a legal system ostensibly exists to do.

A slippery slope in what direction? In the direction of too many rules being illegal or too many things that could impede organizing being allowed?