Wanna get more pissed @ the tax code, look up "clergy" rules

I have someone in my family that works as a mid level staffer in a large church. While discussing their tax situation and the new tax laws, they mentioned that they have opted out of social security so they arent paying in the 6.5% and are doing so b/c church employees are allowed to do so under law if they deem it "against their religion". Now obviously they wont get SS in retirement, but if invested well, that's a ton of money of 30 or 40 yrs that they're not paying in every week. Also, they get whats called a "housing allowance" in which they get money that is deemed "tax free" from income taxes to pay for their home and any upgrades or repairs needed throughout the year. So they actually said part of their kitchen remodel was paid for out of this tax free money. I love them, they are family, but the tax advantages people get for being "clergy" and lets not get confused here, they work in the church, they arent the pastor, so how many people around the country are taking advantage of these loopholes?