In reply to:

the simple rule in English is that you can always use the indicative


Well yes, that may be true. The indicative will give you English that is understandable (which is the first desideratum), but not English that is elegant (which some people don't give a damn about). It's like I said in a previous post -- it's not that difficult to learn a rudimentary English by which you can communcate, but learning it well (well enough to produce elegant prose) is extremely difficult. If students (and others) don't want to take the time and trouble to learn all those goopy rules about indicative vs. subjunctive and others ad nauseam , elegant English is going to keep getting rarer and rarer. There are some of us who bemoan the fact that no one writes like Jane Austen any more.