Counterpoints:
1. Lost and found stations at events. People find stuff, people nearby don't claim it and often don't care if it's taken, but the finder still makes the effort to give it to lost and found or staff. Everytime I've done this, there've been a lot of unclaimed items. Each of those is evidence of, if not altruism, at least morality.
2. The vast majority of people don't shoplift, even at stores that put goods out front with no employees watching.
3. Charities, soup kitchens, anonymous donors.
We should be careful to not mistake cynicism as wisdom.
The reason why Chrome waited for so long to add extensions was the danger they posed to users. I was at Google when Sergey often worried about what extensions would do to non technical and older users who get tricked into installing them, then I saw first hand that danger with my own grandparents. They had extensions intercepting every network request, redirecting certain sites to fake sites, and injecting code into pages. It was horrifying, and they were lucky that they didn't have significant money or identity theft.
Offering something then taking it away is materially different from never having offered it at all.