<late to the party>
Since escaping the underworld and Loot Island rewards you with Uber, Critboost, a speed buff, and (I think) an HP buff, killing players to prevent them from doing such constitutes a tactical decision IMO. This is only marginally a dick move on Loot Island, which gives you the Dive Into A Good Book achievement, which in turn gives you the Bombnomicon item, the first time you escape. Also of note is the medium HP pack in the underworld directly adjacent to two pumpkin bombs, which AFAIK is sufficient to kill all classes -- risk/reward. Thus I am against making such a policy.
Re: Killing people while they're occupied with Monoculous, I couldn't care less either way.
</late to the party>