If someone with MQ who can see everything on the map zones in, they can see from across the zone a huge pile of green and rather than assuming at first glance the pile-maker may just be in the zone stationary or afk, it's a dead giveaway they are active and that will draw the attention of some...even if not everyone. When you see no corpses at all, you don't look at the map and see a ton of green immediately catching your attention. Beyond that, there are many people who will just loot everything and then destroy things or sell later on. I do understand your point that having ZERO corpses around an actively killing person may seem suspicious if you are standing next to them watching them kill in real-time (not a normal scenario for safe MQers), but - in my humble opinion - it doesn't set off nearly as many red flags as the huge pile of corpses sitting there flagging them both on the map and for those people who may be running by. People can also walk up and /con corpses to get an idea of how recently you were there, in case you try to pretend to go AFK when they approach...or for those who have their tripwires set to do such a thing.
Ultimately, it's obvious to see that there are people with arguments on both sides of this discussion and that's why it's a great thing to have a tool in place that allows each individual player to decide for themselves what will give them personally the greatest peace of mind. Having the option to do either, a person can make the choice to delete MOST corpses as they go, none, or all...and therefore feel safer which the approach they feel best for their own circumstances. Personally, if I ever see someone with no corpses around, I've always just assumed their EQ loot filters (part of the natural game) were handling looting for them. I've never stopped to wonder what type of "extra" looting mechanism might be in place to make happen what EQ will do automatically on it's own. People tend to play in groups (even if boxing) and that allows as many players as they have to be looting...more reason to not be suspicious if all their kills are actually being looted as well.
I don't personally see the value in intentionally littering the floor around your toons with corpses, but for those who think that will look more realistic for whatever their reasons, it's good they have the choice to delete whatever they'd like and then CHOOSE to leave certain loots on the mobs to create a few corpses and thus the impression they'd like to make on anyone else in the zone with them. Someone hiding corpses for themselves has really nothing to do with the safety aspect/concern. It's really a suggestion for those who just personally don't want to see corpses or need such a suggestion for lag/performance issues.
I think the best solution to this debate is always ensuring that each individual player always has a working tool in place to make these decisions for themselves and their own situation.