TL;DR 44 pages of discussion.
I would love to see a DZ w/o PVP, but AFAIK it's the only place where SHADE agents can activate the Rogue protocol (except for Aaron Keener and few other agents, lol).
The problem then would be having a DZ which actually is not a DZ since you can't go rogue. Weird. Shall we call it Gray Zone instead? (/jk)
The key problem is that the DZ offers a much better reward than the LZ, so at some point you won't be able to avoid going there once you need high-level gear which you wouldn't find elsewhere. Think about exotic weapons in D1: you could find them in LZ, but at what drop rate? The only realistic way was to play campaign missions at insane difficulty and face AI hunters.