Personally, I think we (as a species) give far more reverence to the dead than they warrant, but I completely accept that this is a sensitive topic for some people and that I'm an extreme outlier here. I see no problem with grave re-use, mass cremations or burials, or really any other disposal method; as far as I'm concerned the only factor that really needs to be taken into account is sanitation. If someone was important enough to warrant a permanent monument, build one, but the insistence that that monument exist over the physical place where their remains once existed feels pointless to me.

Cremation is certainly preferable to graveyards, though. That's always just felt like an immense waste of space, to me.