I'm with you, crystal pvp is terrible and only works when the maps built for it. If it's banned on the server, use the banhammer. you could also make them unabtainable by getting rid of an entire ingrediant. Plus it'll add some depth and story to the struggle. Supply and demand that kind of thing. Just remove all blaze spawners, that'll remove any eye of enders, only downside is that you won't be able to use blaze rods and powder, so just secure the farms. Honestly there's no good way to explain to a friend why something is banned other than saying it is.

You have 30 million blocks, and 200-400 block gaps, you just need to raid 75,000-150,000 nether fortresses to guarantee the removal of end crystals. Fun challange. Or you could just go to each fortress in easonable distance.