I once read long ago Immanuel Kant came up with a model of Maxim. What I interpreted of it is basically that "if everyone does this and it still works in the long run, then it is right."
This makes it easy to portray how some things can be wrong and right without getting too semantic about it. "If everyone litters, things stop working; if everyone decides to steal from another person, things stop working." etc.
Sometimes, however, things are not so simple using this interpretation of mine. A modern example of a solution for invasive web advertisement:
Ads vary. They are often intrusive, sometimes even virulent. Blocking them is defensive and something you'd want your loved ones to do. However they also power a lot of the internet. If everyone uses it, then the solution to Ads will either break, or mutate into another, greater problem.
If someone asks for help with a problem, is it moral to not provide a solution that does not scale?
Obviously you may explain why one shouldn't do it, why be responsible etc. Let's assume however, for the sake of argument, the individual will liberally use it regardless and perhaps even spread it further in the case they are introduced to it.