hmm. that is unfortunate.
i think if i lived in a place in fear of someone draining the oil out of my car for spite, i'd have to consider relocating to another place where social morals were such that it would discourage senseless things like that.
i can't say that i've ever even heard of draining the oil on a car out of spite. i think here if anyone were caught doing something like that they'd probably be beaten fairly severely. vandalism of any kind to a car doesn't tend to happen very often. and i wouldn't think that the addition of a fumoto valve to the oil pan would increase the liklihood of that particular type of vandalism by any measurable degree. i'm not sure anyone would even know you had the valve installed.
anyway, if you did indeed want to put a valve on the oil drain, i don't think fear of vandalism is reason enough, in and of itself, to not do it.