No, it's not the best feature of FOnline. Making this a bannable offense, is not the answer to the problem either. If anything, it should be made harder to do instead.
It bugs me when I see people on here complaining about mercs. As we see in this thread, mercs are not an uber-unstoppable force that players make them out to be. What most people don't understand, is the risks, and losses a merc leader takes. Especially if that merc leader is not in a massive TC faction, and dosen't have limitless caps to spend on them.
So when I loose all my mercs, I take a pretty big hit. Not only must I spend all day crafting psycho to sell on the forum to buy new mercs(This supports player driven economy), I must also re-arm them with the expensive, and hard to find plasma rifle that I often buy from players. And what about the player(s) that killed me and my mercs? They get very nice loot/rewards for killing me and my mercs, compared to just killing a lone player without mercs. So with mercs you are harder to kill, but not impossible to kill, take higher risks, and give players better loot for killing you. This, IMO, Is a good system.