Author is basically very scared of DSA, because he knows that it's ready for power politics on their own terms.
When you are socially conservative but economically left wing, you are going to spend your debates arguing with a right wing / center guy who has 60 "non-partisan" studies about why liberal economics are good.
When you are in the DSA, you evacuate the question by mentioning Gaza at will. DSA is basically an American version of the french LFI, and they are constantly able to stonewall or turn any debate by going to moral issues.