One wrong is greater than another? In this instance, no. Neither own the network, both are abusing it in their own ways.
It's no more abusive than effectively shutting up an overly-noisy diner in a restaurant (minus using actual violence to do so, that is).
I like hat you did there, with the ripped movies/porn reference. Cause those are the only things people do with bittorrent, right?
Nice try, but I mentioned one other example as well - fact is though, most people use BT in a coffeeshop or such specifically to hide their IP addy (or at least avoid having their ISP get the notice, whereupon their home internet would get shut off.) There's only one real reason why someone would actively want to not have their home IP addy tied to the activity. You're kidding yourself if you think otherwise.
If it can knock a bittorrent user off the network, it can knock anyone off the network.
A pickup truck can be used as a mode of transportation, or it can be used to mow down pedestrians. Your point?
This tool will work for maybe a few weeks before torrent clients upgrade to defend against it. Probably by doing the same thing but redirecting ALL local traffic to the bittorrent user instead.
Perhaps, though you should be aware that most BT client devs are emphatically not going to incorporate such a thing into their apps - they have a hard enough time justifying their products as legal devices (to a largely ignorant public) as it is. Anything that gives the RI/MPAA ammunition to lobby against such apps is something they actively avoid providing.
Here's a better idea: how about if you're going to use BT on a network that you don't pay the bills for, you first learn enough about it to configure the thing to be polite on the network? That way business owners and frustrated laptop users won't be tempted to start using this little tool.