Reducing player interaction, well, some would/could argue that an Open PVE group would increase player interaction of a non confrontational kind, it's a valid argument. It also depends on the type of interaction involved, reducing PVP for those that do not want it is a positive not a negative, there are definitely two sides to this coin.
As for your original point, the current PVE groups are a sticking plaster, nothing more, they lack the tools, functionality and clear rules that an open PVE mode would offer. Currently an infiltration into say the Mobius group is in a grey area, because Frontier don't want to deal with the prevention of such incursions and alll Mobius and the group admins can do is deal with the symptoms and not the cause. As you stated earlier, there will still probably be incursions and unwanted PVP, I concede that point, but as I said, making it harder for those that intrude, having clear rules laid out by Frontier and not 'Joe Bloggs - group creator' would help. At least then when rules were broken Frontier would be more inclined to frown upon such incursions and act accordingly.