What did Poincaré mean whe he said:
Later generations will regard Mengenlehre (set theory) as a disease from which one has recovered.
Apparently he also says:
There is no actual infinity, the Cantorians have forgotten that, and they have fallen into contradiction. It is true that Cantorism rendered services, but that was when it was applied to a real problem whose terms were clearly defined, and we could walk safely. Logisticians as Cantorians have forgotten. (Poincaré 1908: 212–213; 1913b: 484)
Poincaré was a very good mathematician so I wonder whether there are foundational reasons for these statements. I'm particularly interested in the kinds of weaknesses he might see in set theory as a mathematical theory.