Yeah they just use their tentacles to catch prey and bring it into their body cavity, where they feed on and defecate out of the same opening. Maybe they don't because they lack the intellect to do so, not because they have any sense of morality.

Well not sure where the disgust for jellyfish is coming from but there isn't really much of a moral argument here. What you are saying is akin to: look you just ate a burger, what's next–the holocaust?

(The organisation of the functioning of bodily orifices of the organism isn't really at all relevant for that. One might also add, that in the case of the burger, there might actually be an argument for some structural analogy that depends on the origin of the meat in a process of captivity and killing, that is organized in an industrial fashion..)