I think you're incorrect (and perhaps a little paranoid) about this being, as you say,

'...the conservative social media strategy in action -- repeat talking points to divert discussion whenever "their side" is criticized.'

tomp isn't trying to change the subject. Instead he asks a valid moral question: why would someone refuse to visit the USA because of Trump's (comparatively insignificant) executive order, yet the same person not be put off by a far more morally repugnant act: Obama's killing of thousands with drone attacks.

tomp also has a strong argument in his comment below about hypocrisy. I'd want him on my team in a debate - he sounds like an honest man.