The EO is cruel and irrational and is something I'm firmly against. It makes sense to not host your conference in the USA for moral reasons.

But, on the other hand, a lot of Americans don't have passports or their employment contracts will only reimburse a number of domestic (non-international) conferences a year. The set of those people who would be excluded probably exceeds the set of attendees from the 7 countries in question. So I'm not convinced it makes sense to do this just from a conference attendance standpoint.