Of course IV does not only make revenue by litigation, they also make revenue by licensing patents without litigation. If the patent system were not broken this would be a perfectly reasonable business model, funding new inventions and selling the rights to produce them (which of course would require litigation if people produced those inventions without paying). For your argument to be valid you must establish that not only is the current patent system broken, but that it would be fundamentally impossible to have a non-broken patent system.