I must buy car insurance to drive: it's the law, and there are criminal penalties for violating it. But that doesn't make it a tax.
The fact that the return is poor changes nothing. The fact that the government has borrowed and squandered most of it changes nothing. The fact that it's mandated changes nothing.
If you want to be on the side of politicians who make a shameful claim that "everybody who works pays federal taxes," that's fine with me. But it's a lie: 1/2 of the people who work in this country make no contribution to America. That is the fact.
Right there is the nut of the controversy. Some say SocSec collects money to be used by contributors and most people here see it as a Ponzi scam for gov't spending. Two reasons make me favor the second theory over the first. One is that SocSec taxes have always been more than SocSec disbursements with surplus being immediately spent elsewhere. The other is that whenever governments reach the 'zero excess' point they slash/eliminate the program.
The money is collected to support the government, and payouts to contributors is held at the minimum needed to keep the scam going.