[the man what to eat that fruit.]

You're right, the map developers did not intend for anyone to use the grapple hook in general, especially to reach that area of the map, so dont do it, that is exploiting the map.

I really don't understand, what's the difference between using the grappling hook to hide under the airship and using the grappling hook on terrortown to get to an inaccessible roof? Why is one considered and exploit and the other one is totally fine, even though the terrortown thing is infinitely worse because you can actually kill people from those rooftops. The issue lies with the grappling hook, you can't say it's okay to use it sometimes and forbidden to use it other times, it just doesn't make any sense. 

Either remove the grappling hook or let people use it as they see fit.