"That "no" means they have to be willing to replace a substantial amount of their employees"

Not if many of them are afraid of being fired by speaking up. You know, the very people who need a union.

"Unions are an incredible tool, and I'm in favor of them. That doesn't mean I'm in favor of laws enshrining them into disproportionately more power than they already wield."

But without those laws, they have no power. So you've just admitted you are not in favor of unions.