If I was a purist I'd say "no". Using those weapons might be.

Not being a purist I'm happy to make exceptions for probable use or effect of the activity. So:

Selling weapons to people likely to commit crimes is a reasonable exception to the simple version above. and Prostitution, where the probable outcome is a mutually satisfying service involving ONLY the parties involved is not a reasonable exception.

> But in cases when it's a choice freely made by all parties concerned ...

Presumably the targets of isis’s weapons are “parties” and don’t want to be shot at.

Then again, what about hiring police: the robber is a “party” too and presumably does not consent to being caught!