Paying for food as a captive audience is very mature? I guess I'm glad to be childish :)
The "free" food is obviously paid for by the company with money that could otherwise go to salaries.
If everyone got higher salaries and food was charged for, then you could make choices about spending money in the cafeteria or saving money bringing food from home. Adults make choices.
By making the decision for you that you'll take the lower salary but get unlimited food, the choice is being made for you, much like a parent decides for a child.
So yes, there's a very strong argument to be made that "free" lunch takes away adult autonomy and is indeed "childish".
Aren't you still capable of eating something that isn't free?
This line of reasoning makes any workplace perk into an act of infantilisation:
401(k) matching? You mean you let them remove that much agency from your investment planning?
Healthcare? I would prefer to be a big girl and buy my healthcare plan on the open market.
Free parking? I'll decide for myself where to park since I'm an adult.
Nice toilet paper in the bathroom? Do you think I can't provide toiletries for myself? That money could have been salaries.
I suspect part of the percieved value is that by making lunch a communal event, rather than everyone grabbing 30 minutes sometime between 10:45 and 14:30, means it's also a time for face time outside of group lines. If you need to talk to someone on another team, you usually have a chance to make contact at lunch.
Furthermore, many of the tech campuses in the south bay don't have enough restaurants nearby to support all of their employees going out to eat lunch.
There's also something to be said for just grabbing lunch at the cafeteria with your colleagues as opposed to figuring out where to go eat, driving there, waiting for the order, eating, then driving back.
If that food money is transferred to salaries, the 'free market' will do everything in its power to suck all of that money by giving the minimum in return in order to maximize profit. Because that's what it does. It will cost both the organization and the employees more.