If someone shows up with no supplies and no firearms knowledge, I wouldn't immediately classify them as useless. There's a lot more to a SHTF situation than standing guard with your gun. Even the most basic of things: you might need people to cook, people to gather water, gather and chop firewood, watch your back while you fix the generator, etc.
Even if the person's sole responsibility was staying awake and watching for strangers approaching the house while you get a few hours of sleep, that would make them more than useless.
Bottom line is that, as long as it wouldn't put my family in danger or dangerously low on supplies, I wouldn't turn any friend away. And I certainly don't think that political views is a valid way to determine who to let in and who to turn away. Now if you think that they would be a danger to you, or if you simply don't have enough space or supplies to accommodate them, then turn them away.
Even if the person's sole responsibility was staying awake and watching for strangers approaching the house while you get a few hours of sleep, that would make them more than useless.
Bottom line is that, as long as it wouldn't put my family in danger or dangerously low on supplies, I wouldn't turn any friend away. And I certainly don't think that political views is a valid way to determine who to let in and who to turn away. Now if you think that they would be a danger to you, or if you simply don't have enough space or supplies to accommodate them, then turn them away.