Metronomes have been around and widely used long enough to have proved their usefulness beyond any reasonable doubt, I reckon. Certainly not all music should be played 'strict tempo', but any musician worth their salt should know the difference, be able to do either, and be aware of it. Long observation has told me that hatred of metronomes is generally inversely proportional to the natural rhythmical skill of the player.

Habitual foot tapping is nearly always counter-productive as the foot invariably follows the timing errors and reinforces the bad habit. The one exception to that being when the player already has an excellent sense of rhythm and timing. Obviously the best way to determine that is to try playing with a metronome.