You must have income to contribute to a Roth IRA. That income cannot be passive or SSI based. If you have W-2 type income you can choose to take an immediate write-off with an IRA contribution or you can choose to pay taxes now and after that, never pay any taxes on that money again. That choice should be based on your age and your tax bracket.
Example: A married coupe filing jointly and making less than $79,000 a year is only paying 12% federal tax rate. To me, it makes more sense to pay the 12% now and have $6,000 grow over time tax free. In 20 years that $6,000 will grow to $28,000 using the historical return of the SPX. In 40 years it will be $130,000.
As you can see, the answer is based on your circumstance. If someone is in a high tax bracket it may not make sense.
Also, people who plow all of their assets into a 401k for 40 year may find they're in a very high tax bracket when they retire.
One other idea. If a parent has children with income the parent can fully fund a Roth IRA for the kids.
