i think its only negative in manhwa bc its in the context of friends where at least one probably has feelings for the other. so they inherently dont like it bc theres the expectation that the relationship (like the benefits aspect not necessarily the firends aspect) can end when the other person finds a romantic partner. so theres like an undercurrent of possessiveness without the justification necessary to express it
When i was younger, FWB benefits meant someone wanted a relationship and someone didnt, so they compromised and just had sex, resulting in the one with feelings getting consistently hurt over time. Even when it worked, FWB mostly ended up just being about the benefits without any actual friendship.
I finally have a FWB which actually is a friend... with benefits. But it took forever to get find someone who was capable of operating that way.

why does 'friends with benefits' have such a negative stigma everywhere whats wrong w fucking your friend