This is what happens when people with zero understanding of the protocol starts talking about it. If you half block generation time, u'll increase the orphan rate, reduce block halving time and ultimately end up with an alt coin.
Well lets step back and look at that statement. I don't have zero understanding of the protocol, but I do have a limited understand I'll admit. It seems that most users, and posters on this forum, are in the same position. We are here to learn, and I hope that I will get some explanations as to why I am wrong, if I am wrong. Looking at Bitcoin from a commercial point of view, an average block interval of 10 minutes is way to long. This is regarless of any technical issues.
Now lets look at the technical point you made. Block generation averages a ten minute interval. That means sometimes it is a lot longer than 10 minutes, as in the two hour period I mentioned. Now the system will need to catch up on a period when generation had a 20 minute interval. That means it will need to run with 5 minute intervals for a while. This is the current system that will have to cope with that, and it doesn't seem to create more orphans. Of course halving the block generation time will create more blocks, so you would have to adjust the miners reward to compensate for this. I don't see why this would create an alt coin. It's still Bitcoin, and it is still using the current blockchain without any alterations.