No, not if we want the program to remain solvent. And I'm not sure what this would accomplish. My assumption is, the type of people who would opt out would be the very people who do not save enough for retirement now (lower wage earners who are not very adept financially). Letting these people opt out would put another $30 or whatever in their pockets every pay period. But when it came time for them to retire (65 or so), they'd wind up collecting SSI/Supplemental Security Income (which is funded by general tax revenues) instead of Social Security. So the tax payers would have to make up the difference for those who did not pay in, but whose assets and retirement income qualify them for SSI.
IMO, what we should be doing is taking a closer (albeit painful) look at who is eligible for Social Security benefits. I'm FAR from any sort of expert on SS. But one issue I see is the number of people who are able to draw a SS check based on the earnings of just one person. If you take a guy (or gal, but usually it's a man) who has been married two or three times, at least 7 years (I believe) to each woman, by the time they all reach retirement age, you could have three or four people drawing benefits, when maybe only one of them ever had a job or paid into the system. Questions of fairness aside, to me it's a question of simple math.