PayPal does not insure things purchased by F&F, so that arguement by the OP is not valid. When paying for used, preowned items I typically voluntarily send via F&F to save the sender some money. I feel this is well within the spirit of F&F as it is not a commercial or taxable transaction when the item is used, not manufactured by the seller, and sold well below the retail price - there is a legal distinction.
Typically the money goes to the sellers “wallet” (regular or FF) and you have to transfer it to your bank account explicitly. So PayPal makes money off the transaction until that happens, just like a bank, and THAT is why PayPal doesn’t care in those cases.
When I sell I don't care how the buyer pays as the choice on their end is whether they want the added insurance. If neither party wants extra insurance then they should not pay for it. I don’t sweat the difference, and I think you are not allowed to stipulate in your posted adds. On a few occasions I have chosen to use the insured route for high ticket used items like a Burkie, and in one case where a guy said he would reduce the price if I did the FF method I said go ahead and send the rod regular, and I will pay more and split the difference with him.
On very low ticket items like $10, where I was basically just trying to get things to people who could use them as a good deed, and where I was on the cutting edge of loosing money after shipping, I have suggested privately to the buyer that they use FF, but said that it was up to them. The only guy that still payed regular was not coincidentally the guy who was trying to bargain me down on a used $4 item that sold for $25 commercially. I lost money on the whole transaction, but didn’t care.
Doorstep or not? This is an issue for the buyer to bring up. For me for example doorstep is FAR better than back to the PO. Don’t presume to make this decision for the buyer. Ask before you send if it is an expensive item, yes. But with modern online tracking it is easier to watch for the arrival of expensive items.
PayPal makes an enormous amount of money off of me. It is my preferred way to pay for things online, commercial and privately and I hardly use my CC anymore. My fishing buddies and I even typically pay each other back via PayPal for our shares on fishing trips now, rather than writing checks.
Personally I feel all Speypages members are my friends.