There's nothing wrong with the idea of having multirole aircraft. Hell, the EuroFighter was originally designed as an air superiority fighter, but is used for a

There's nothing wrong with the idea of having multirole aircraft. Hell, the EuroFighter was originally designed as an air superiority fighter, but is used for a variety of ground attack missions as well. And the F-35 isn't intended to replace the B2 Spirit stealth bomber, nor the A-10 (though the USAF would really like to); it is meant to replace the F/A-18 and F-15, which are themselves multirole aircraft. The issue with the F-35 isn't that it is intended to perform both air superiority and ground attack missions. The basic objection to the F-35 is designing a single airframe with several variants capable of conventional takeoff and landing (F35-A), short takeoff and vertical landing (F35-B), and catapult assisted takeoff and arrested recovery (F35-C). These are completely different ways of taking off and landing, with different design constraints, and it is difficult to create an airframe that can be modified to perform any of them. That's the primary philosophical objection to the F35, at least. There's another whole debate about whether we need aircraft dedicated for the close air support role (like the A-10), and the rest of the complaints are specific to F35 design choices.