Basically that religion is a huge part of the culture. The year of a lot of cultures revolves around major religious holidays, christmas, ramadan etc. It's deeply ingrained into social dynamics, language and so on basically messing with it will cause a huge upset just from the magnitude of the impact it will have on peoples lives. Being part of a religious community is a big part of those peoples lives. Celebrating religious holidays a big affair with the whole family. Also could you imagine western economies without the christmas season? A lot of peoples livelihood depend directly on producing commodities for easter or christmas.

It's also not really something material you can control, people can choose to be religious and teach their kids accordingly no matter what. Where's the boundary to organized religion?

Add to that that it both gives comfort to a lot of people but also makes it hard for them to break with it on the threat of some form of punishment (like opium, dulls pain but once addicted its painful to suddenly stop taking it). I know I wouldn't have survived my depression if not for religion.

So a shock "therapy" banning religion as much as is possible will cause a huge pushback because it's dear to a lot of laborers. It's been used by the bourgeoisie yes, but very indirectly. You can point at how someone withholding the means of production needs to be made to relinquish it, but you have to look at the case of each clergyman individually in how much they collaborated with the capitalist class.

I'm sure someone with a deeper understanding can explain it better but that was the opinion as I saw it and which got me intrigued.