Coetzee sees only the former condemnation without fully appreciating its import ("The Bucky with whom Arnie does not sympathize is haunted by a suspicion that when he said 'Yes, I will flee the city,' the voice that spoke was not that of his daytime self but of some Other within him"). But the second is the more important one, and brings us back to Slavek's choice.
Okay, one might say, and as Arnie suggests, a man like Bucky could not stand the thought of living his life as a burden on Marcia or anybody. Yes, we know he has a psyche that would call for action "on a grand, heroic scale," or we think we know through Arnie's filter. Such people (as Coetzee suggests) can be dangerous. So what? One's propensity to "desperately seek attention" through "grand" moral acts does not, in itself, mean one's act is not morally sound. The residual problem is still whether it is right to live as a burden on the people we love. Roth, like Koestler, complicates things for us but the complexity only makes the simplicity of the moral question feel all the more compelling.