anyone ever campaign a truly GOOD party?

[Unoriginal]

Isn't that a little be flawed, to consider any particular "Good" plane to be the purest form of good? It's not like alignment is some form of bounded-in-sum property (where adding law or chaos to good makes you necessarily less good)--I"m sure that the other planes would strongly disagree that Elysium is the "ultimate plane of Good". It's a plane of Good, for people with particular properties including a general, rebuttable reluctance to engage in violence. Solars are as good as it gets, and they're super non-pacifistic. Same with all the angels. They take much more after the "angel of destruction" motif than the "cherub with harp" motif.

This.

There is no "the one good" in 5e.

The best argument for goodness = pacifism in DnD to me is that Elysium (the ultimate plane of Good unadulterated by other influences) leans heavily that direction... but even there we have specifically combative celestials; and every other Upper Planes has very explicit places and entities who crusade against evil (both in the planes and the prime)

I'm not sure where this "good implies must not kill" thing came from

Even Lulu the Hollyphant will kill you if you attack her.

Good = devoted pacifism has not been a thing in DnD since the mess that the 3.X Book of Exalted Deeds was, as far as I know.