Right up until the FBI asks them to do it for one that Apple does not want to comply with. The danger here is all in the precedent.

Currently, Apple's defense has mostly been "we have no technical ability to decrypt users' phones." This is what protects them from being held in contempt of court when denying court orders to do as such.

If they say "yes he's a terrorist anyways, we can do it just for this one instance," it proves that they can also do it for drug dealers, drug users, political dissidents, journalists – politicians even. You might say "well they'd need a court order, so that wouldn't happen for dissidents/journalists/politicians" and you'd be right... if you were talking exclusively about American dissidents or politicians. Foreign people are offered no such protection, and if Apple creates the ability to target them, you'd be naive to think the FBI/CIA wouldn't leverage it every chance they got.

That's all still under the assumption that every court order is a valid one (a stretch, these days).

This is a bad thing for everyone. Apple should be praised for this stance, it takes serious spine to stand up to both the federal government as well as a population that wants nothing more than to rid itself of terrorism.