The problem is, when you stipulate that criticism has to be “responsible” in order to be permissible, you’re introducing a secondary debate about what “responsible” means in this context. People who disagree with you on object-level claims are more likely to also disagree with you on second-order claims about which statements are “responsible.” Accordingly, second-order requirements like this ought to be loosely and generously applied, recognising that subjective impressions of “responsible” tone can be even harder to agree on than object-level claims.
So let’s apply your requirements, loosely and generously, to the case of Leif Wenar’s article. You have two main points. Firstly, people who agree with TSPG (or “other important neglected truths”) should clarify that up front. Secondly, people should only give the impression that “EAs are stupid and wrong about everything” if they actually believe this, in which case they should explain why they think this is true.
Wenar has done both of these things. I don’t think he agrees with TSPG as EAs apply it in practice, but he does affirm an alternate neglected principle — namely, that of ethical cosmopolitanism. He writes “Hundreds of millions of people were living each day on less than what $2 can buy in America. Fifty thousand people were dying every day from things like malaria and malnutrition. Each of those lives was as important as mine.” He’s also clear that he thinks most Effective Altruists are well-meaning people who sincerely want to help. And, yes, I think he is sincere in believing that EA is wrong about most things. He relates having spent a long time in his own sincere effort to find out what kinds of large-scale international aid are truly effective. His conclusion seems to be that it mostly isn’t.
Accordingly, I think this is best dealt with as an object-level disagreement. Wenar is giving the impression that EAs are foolish and wrong because, based on his own attempts to do what they are doing, he sincerely believes that they are, in fact, foolish and wrong. Calling him “irresponsible” for accurately conveying this belief is missing the point.