Later generations will regard set theory as a disease from which one has recovered.

Ernst Hölder attributed this to Poincaré in 1924: "Poincaré at the Rome Congress (1908) went so far as to say …", but this is not an accurate summary of his remarks in "The Future of Mathematics". See Jeremy Gray, "Did Poincaré say ‘Set theory is a disease’?", The Mathematical Intelligencer, 13:19-22.

Also, probably a variant translation of Hölder's comment, "Point set topology is a disease from which the human race will soon recover."