Paul Unnasch notices the $335 in payroll taxes coming out of his paycheck every month for Social Security, and wishes he could get those dollars back.

“If there was a way to opt out of Social Security, I would,” said Mr. Unnasch, a 27-year-old technical writer who lives in Milwaukee. “I don’t have much trust in it — I know I’ll probably get something out of it, but people are living longer and there’s a huge generation of boomers retiring now.”

An aggressive saver who socks away 20 percent of his pay in retirement accounts, he would prefer to put those Social Security payroll taxes into the stock market or use them to pay down his student loans.

Mr. Unnasch’s take on Social Security isn’t unusual among younger Americans. Research shows that a majority of young people are more pessimistic about the program than their older counterparts are. Gallup polling, for example, shows that just 37 percent of Americans aged 30 to 49 expect to receive Social Security benefits when they retire — compared with 66 percent of people aged 50 or older.

Social Security is not on a course to vanish — but the concerns voiced by young people are understandable.

Last year, the program’s retirement and disability trust funds had reserves of $2.79 trillion, but expenses have been outpacing noninterest revenue since 2010, mainly because of low birthrates that translate into a declining ratio of workers paying into the program and more people drawing benefits. As a result, the trust fund reserves are forecast to be depleted in 2035. At that point, the program would be bringing in enough cash to pay only 83 percent of the benefits promised to current and future beneficiaries, according to the most recent projection of the Social Security trustees. That would be the equivalent of a 17 percent across-the-board cut in benefits.