> this is even problematic with objectively undesirable elements, like the homeless.
Homeless people are sensible and capable people, not "objectively undesirable elements". Also, no one is essentially "homeless" like one is assigned a race or gender based on certain physical characteristics. Homelessness is the disease of a society which has no respect for humans whatsoever, and in which the number of empty dwellings far outweigh the number of homeless people.
Many self-organized communes are built by people who were previously homeless or living in squats. Yes, of course that includes queer and colored folks, and people of different religions. In fact, some previously-homeless folks can be very helpful to a community because they're often used to various forms of mutual aid and doing the best we can with what we have (hacking around stuff).
> But what is a homeless person to do if each and every city outlaws their presence?
We're talking about autonomous communes based on various forms of affinity, not centralized power structures. That's a very different topic.
I may be wrong, but i'm tempted to believe even in most cities, if there were any actual form of democracy, most people would choose to help the homeless (at least in the popular neighborhoods, as research has shown empathy decreases with wealth) because the solution is easy: just take the empty apartments and place homeless people in. Problem solved. As easy as 1-2-3 if you don't care for this tiny piece of paper called "property title" which in our cultures is deemed more important than actual human lives. If that sounds way too radical for you, how about giving some space for people to build their own housing? Many homeless people would be happy to build something if there were not angry blue-uniformed psychopaths tearing it all down whenever they liked it.
But in this topic, we're talking about collective housing on the countryside, which is very adapted for formerly-homeless folks. First, because after years on the streets it can be frightening to suddenly have a place of your own where you have to stay alone. Second, because having people around can help with many physical/psychological/material problems. Third, because taking part in a collective project such as building a commune can be very empowering. Fourth, because getting closer to nature is soothing, especially after a long time struggling for basic survival in the concrete jungle.
But please remember we're talking about a small commune without a mayor, and where consensus (100% of people agree!) is required to kick someone out. It's not exactly kafkaian tyranny. If anything, the rules we're used to on a daily basis are much more unjust and violent. Like the one that says if you don't have enough imaginary numbers (money) to give to an arbitrary person (landlord) then heavily-armed puppets (cops) will tear down your door and evict you at gunpoint. That's the kind of ordinary injustice and violence which does not exist in free communes.
If you still think excluding someone from a community is oppressive, you might want to take a step back and look around you at the evil barbarism lying at the roots of capitalist society.