It's not about Google, it's about OP's personal values
It's one phone's worth of demand either way.
First hand = money goes directly to Google including margin
Second hand = money only goes towards a private person, 0$ for google. At best it prevents usable phones being thrown into landfill.
Right. And if you buy a secondhand one you are increasing their value on the secondhand market. Reducing the depreciation increases the value of the brand new phone.
If you don't think voting with your wallet works, then that is a position you can take. But you can't think it works when buying from the OEM but doesn't work when buying on the secondary market.
And ultimately, if buying it on the secondary market in such small numbers that it doesn't move the market, then it adequately addresses the concern.
Edit: I'm not saying there's zero effect of it, but it's likely statistically insignificant.