It’s easy to disparage great art, comparing it to other works. That’s not a reason not to collect it though, writes James Fenton. “Don’t imagine, when you read that some declared expert has spoken out rather forcefully against this Rubens or that Raphael, that this is the first time in history that this daft game of disparagement has been played. Whenever a strong claim is made on behalf of a work of art, there are plenty of dim individuals (inside and outside the art world) who are simply provoked into opposition – offended that something should be admired when they have had no say in the matter.”