Organic agriculture is just growing without chemical fertilizers and pesticides - in other words, the way people farmed for most of 10,000+ years - so for someone to say it's a "pipe dream" is just silly. If you've been growing with chemicals it can be quite difficult to transition to organic because there won't be a living ecosystem in place. Chemical fertilizers can kill beneficial soil fauna, and pesticides often kill both harmful and beneficial insects. So it can take at least a year of organic before a balance of living organisms develops in the garden. During this period yields may be extremely low, and results generally disappointing. But once the organisms recover, results should improve annually.
I think permaculture is quite possible in a small space - you just have to be more careful in what you choose to plant. You certainly don't need acres. My permaculture gardens are quite small.
Simply gardening organically, without permanent crops, is very successful for many people - this is the way most folks here on the board grow their vegs, most only have permanent fruit crops, and maybe some asparagus. Many of the plants we grow as annuals can be perennials in the right climate. For instance, I grow sweet potatoes as perennials, but in areas where the ground freezes they can only be grown as annuals. It's often easier to organise an annual garden, because you can just clear everything away between crops - this helps avoid persistent weed problems especially. Though it can help avoid persistent pest problems, clearing everything away also clears away beneficial insects, as well as pests. With permaculture, it's harder to change your mind about plant placement. So for most people, it might be easer to start gardening using basic organic techniques, and then gradually transition to permaculture. This is what I've been doing.
Folks who say you have to use every "correct principle" in their favored method are being too dogmatic, in my opinion. It's possible to get just fine results using a variety of techniques. The main thing about "permaculture" as opposed to other methods is permaculture is a set of ethical principles as well as techniques. The techniques themselves are nothing new, what's new is the organization of them with the ethical principles into a holistic design system.