Well, not sure it was you, but the harpoon idea seems ripe for abuse.
It would entirely depend on how it was implemented.
All I want, is a way to stop ships that already have their thrusters down.
As they have their thrusters down when this thing is useful, it's exactly as things stand now - but you can stop things that are already helpless.
If their thrusters come online, they can pull the harpoon or whatever it is out of their ship and continue as though it didn't exist.
I'd settle for just making it so that ships come to a stop when their thrusters blow out (as they do when the power plant blows out, in case anyone wonders about "realism" in a game with friction in space
I do wonder what abuse you were thinking of though, as I'm pretty sure whatever it is, already exists in some form.
If it's people holding you in place forever - well, welcome to shooting the thrusters just as they are coming back online - for instance.