I don't think there's any problem with a "friendly" horse...I've had my fair share of dealing with nasty horses! However, for me there's a big difference with being "friendly" and being disrespectful. I want a horse that will not enter my "space" or "bubble" unless I invite him (or her) to do so. I also don't want a horse that rubs it's face all over me or pushes me with its head. I definitely like my horse to come to me when I call or go out to catch it, but I also want my horse to be focused on me and my actions, to move when I move, follow me peacefully, and to watch ME in scary situations to see my reaction. IMO, this makes for a much calmer and willing horse. Nothing wrong with friendly, I just want to make sure I'm respected too. I do still enjoy rubbing up on my horses every now and then.
There was a day when my family treated horses like dogs. We still have one really old gelding who acts like a dog, but I trust him 100% (I don't know if I would EVER trust another horse as much as I trust this guy). He's been around the block (literally) a million times. He has no concept of personal space, but with his personality it's never been an issue. Now that I've gotten more into the treating a horse like a horse mentality, I don't really see my horses as pets anymore, but more as animals in my herd. Treating my horses like they would be treated in a herd has really helped me in my training (Of both myself AND my horses!). It's much easier to understand horse behavior when you mimic their actions.
I went off topic a bit, but I really don't see a problem with a friendly, but respectful horse. If a horse is constantly allowed to butt into others' personal space, they tend to think they are in charge, and that can cause some real issues with certain horses.