I thought about that. In fact, I even had a couple of suggestions typed up. But then I decided it might destract from the message to ATM newcomers.

I suppose my big suggestion for ATM responders would not to be in too big a rush to declare an alternative idea wrong. Yes - sometimes an alternative is way out there. But if the ATM proponent doesn't have the opportunity to fully explain and try to defend the idea before they are told it is wrong, they are more likely to feel that they are not getting a fair hearing. It would probably be a good idea to ask probing questions before shredding the idea completely. Let the ATM supporter spell out a lot of their thinking - and then clearly explain where the idea fails.

And a very similar suggestion. If the alternative has an outside chance of being right, then it might be better to acknowledge that the slim chance does exist rather than insist the theories chances are so small as to not be worth discussing.

Something like ... "I'm not convinced and consider this idea very unlikely, but we need more evidence (possibly offer a few suggestions/examples) to be absolutely sure it is incorrect." ...should leave the rational ATM supporter feeling like at least their case was heard. It might even spur them to dig deeper into the knowledge base. I know I've seen the BA make statements like that before.

And from my own experience, my aggravation when discussing Arp's model/Intrinsic redshifts comes not from other people being unconvinced. That I understand and have no issue with. But I do get annoyed when some people express misconceptions about the model, then describe it as pseudoscienctific terms, and finally treat it as quackery unworthy of discussion.