I agree that both psych and physical force have appeal, for me it just depends on which button I need pushed. The concept of physical forcefeeding (whether realistic or fantasy) usually satisfies the aversion I have to not gaining weight; that there is absolutely no way I can prevent it.
When it's psychological/social, that tends the satisfy the part of me that wants to give in and be stuffed and/or stuff myself with abandon, but again it's mostly about what the feeder wants to accomplish.
Acts that I would consider psychological force-feeding are manipulation ("I made these just for you! Are you going to let them go to waste?" "I noticed you really liked this recipe so I made a dozen!" "Oh I'm finished, here, have the rest of my plate."
or conditioning, such as just always having snacks/drinks on hand and rewarding not just went I eat but over-eat, finishing with lots of fun sexytimes when I reach my absolute limits, etc. Another particular favorite is to be given a time test, such as to eat continuously for an entire hour or have a certain window to finish a meal.
(Blackmail is also a hot button for me but that's a whole different topic, really!)
It's still my choice to put the food in my mouth (or have it BE put in my mouth and I eat it) but definitely to satisfy the feeders' desires. For me personally the feedism is about a full stomach and giving up control to someone, as I'm very much in control of the rest of my daily life.