That’s what a 401(k) is though. If it’s unknowing then they just know it’s a savings account. Being mad you weren’t told that fact is like being mad you weren’t told your health insurance involved giving some of your paycheck to a third party who will only give some back if you get sick.

Pensions I agree with you there, pensions are a black box where you put money in, they decide how to manage it, and money comes back out when you’re old

Most of boomers will have their 401k (unknowingly) invested into the stock market by their employers

That’s not a 401(k) is. A 401(k) is just a regular investment account that has special rules around taxes because it’s meant to be cashed out when you retire. Everything in a 401(k) is in the stock market (though it can include bonds, mutual funds, etc. too), and none of it is managed by the employer. The employer just makes contributions that the employee decides how to manage.

It’s entirely possible that people don’t understand their 401(k)s, and that the employer went with a full service broker that manages the 401(k)s on behalf of the employees. But, it’s not possible for the employer to invest 401(k)s into the stock market because the employer simply makes cash contributions and then it’s hands off.

Pensions are different. Pensions are things where the company agrees to pay the employee a certain amount when they retire. In that case the employer is definitely investing in the stock market – although, in this case, they almost certainly hire a company to manage it for them.