I think Sean's article takes apart the SP's line on the middle east bit by bit, and with little effort because he's been doing it since England won the World Cup. But that's not what Mark P is arguing about, not surprisingly.
Instead he thinks the AWL is too argumentative, too honest maybe. This, and the "sideshow circus" line, is a variant of the Grantite "sects on the fringes of the labour movement" riff used to warn off Militant/SP members from straying from "the Marxists" in the labour movement. Instead the SP, like the SWP, do their dirty factional work behind closed doors.