"Some union officers even say right-to-work helps their recruitment efforts. Gary Casteel, now the UAW secretary-treasurer, said in 2014, when he was in charge of organizing Southern auto plants, “This is something I’ve never understood, that people think right-to-work hurts unions.”
“To me,” he continued, “it helps them. You don’t have to belong if you don’t want to. So if I go to an organizing drive, I can tell these workers, ‘If you don’t like this arrangement, you don’t have to belong.’ Versus, ‘If we get 50 percent of you, then all of you have to belong, whether you like to or not.’ I don’t even like the way that sounds, because it’s a voluntary system, and if you don’t think the system’s earning its keep, then you don’t have to pay.”
https://www.mackinac.org/v2016-18
That's true. I personally used that line when organizing my work place quite often. It was a big selling point to workers on the fence.