If I invite a non-pilot pax, I certainly don't ask for a contribution, but will accept one if it is offered, and is within the rules. Sometimes the offer is made, sometimes not. Neither affects my opinion of the pax.
If I'm asked by a non-pilot pax, then I would explain the costs and suggest a (legal) contribution - but certainly not if the pax were a youngster, they should be encouraged, as I was. I guess if the person asking for a trip then refused any contribution, that might well affect my opinion of them....
With my PPL friends-and-colleagues we operate an 'unwritten' rule of neither asking for nor offering payment for pax time; as we frequently invite each other for pax flights it usually evens up over time. However, the talking-freight usually buys the coffees, the bacon butties, and pays the landing fee.
Just occasionally it's good for the soul to do a completely solo flight, but usually I would much rather fill a spare-seat.
Interestingly I believe it is legal to equally share the full rental cost of a hired aeroplane, but an owner can only share the direct hourly costs such as fuel, and not any part of the fixed costs such as hangarage, insurance etc.
Slip