Leftists all recognize the Laffer Curve, just not its fiscal significance. This they deny because of their belief in Keynesian economics.
However, they're forever trying to "modify behavior" through tax policy - higher taxes on cigarettes = less smoking; higher taxes on gasoline = less driving and buying fuel "efficient" cars; etc, etc, etc.
This is their Achilles's Heel, though, because it puts them in a self-contradictory position. They believe tax policy does change behavior in predictable ways when it suits their agenda, but not when it doesn't.
Heck, "progressive" tax policy itself is a recognition of the Laffer Curve.