Don't worry about it, I don't hold grudges over stuff like this ^_^ I get defensive too, so I understand. Glad to see you've made the smart decision to house them separately, and I hope you can convince your friend to do the same. If I were you I'd just forward him this thread.
Just think, the money he'll be spending in buying tubs/building full enclosures will be FAR cheaper than the money he'll be spending in vet bills.