I notice "argument from personal ignorance" is common in "believer" circles (not just of aliens, but of all kinds of conspiracy theories). If you happen to be well educated enough to provide a detailed explanation of why a particular thing they've said doesn't hold water, it's frustratingly common for them to fall back on "well I'm not an expert, I don't know all the details, I'm just asking questions." Somehow it never occurs to them not to make wild assertions when they "don't know all the details".