There is no blank exemption from social security.
But - you are correct - you can request an exemption from SE tax if you are a member of the clergy (minister, member of a religious order, or Christian Science practitioner or reader) or a member of a recognized religious sect.
To request exemption from SE tax, file Form 4361 in triplicate (original and two copies) with the IRS.
When you do so - you certify that that you are opposed to, the acceptance (for services performed as a minister) of any public insurance that makes payments in the event of death, disability, old age, or retirement, etc...
So you do that NOT based on possible benefits - but based on your believes.
After approval - that will be very hard to revert back.
As anything else - there are some advantages and disadvantages of such decision.
First of all I personally do not believe that the Social Security program will be eliminated... It must be reformed - that is correct - but one way or another - we still will have such program.
Then - it may be viewed as insurance - which pay back under certain circumstances - and if your church may afford to establish separate retirement plan and medical insurance for you - so you would not need any government coverage - that is something you may consider.
On the other hand - that is very personal decision...