I took in a package for the neighbour today and when I took it over she offered me a glass of wine... yes please. She then rushed at me with a coaster when she noticed I was about to put it down on the side table.
Coasters are to prevent condensation from marring the table. The foot of a stemmed glass will not have condensation. All a coaster does when a stemmed glass is involved is to make an unstable target for putting down something that is already top-heavy. It really is alarmingly stupid.