The mutants don’t have to touch Terrigen at all, which means the problem is really of a limited scale to them. So, the idea that the Inhumans should destroy their entire (20,000+ years) cultural legacy because mutants have a problem with Terrigen… I think it’s understandable that they would take a wait-and-see approach, and try to find another solution.
To explain another way — there are kids with deadly peanut allergies. We don’t implement a worldwide ban on peanut butter or Snickers. We just make sure those particular kids stay away from peanuts. This is that exact situation. Now, we’ll see what happens in “IvX”…