Ministers and Social Security Exemption

What is the wisdom out there? A letter from a reader:

I was recently asked by one of my students, who has just taken a ministry position, whether she should petition for exemption. The form one has to sign for the IRS says:

“I certify that I am conscientiously opposed to, or because of my religious principles I am opposed to, the acceptance (for services I perform as a minister, member of religious order not under a vow of poverty, or a Christian Science practitioner) of any public insurance that makes payments…”

I know several who have opted out to keep more of their money, not on specifically religious grounds, beyond a claim that God commands then to care for their family, and they need the money for that.