It is worse because it keeps you completely safe while shopping. Nothing like that is in place at the moment. You can lure people as it is now by letting them know about your vendor in gen chat. If people don't want to get killed or get their stuff stolen there are plenty of shards catering to that exact mentality.How is that worse than a free gate? If as I suggested that you can't do anything besides interact with the vendor, it should have no affect on anything or anyone around you. Making you invulnerable was a suggestion to keep people from grief-ing by luring people into a vendor and then ganking them.
Just because teleporters and portals are broken doesn't mean more broken systems should be added.
That said, I do not like the idea about getting a free gate either. But I would rather remove that all together than making people invulnerable. And as I said, people are already using teleporters to get to key locations. I can't think of anything new game breaking there.