The rules are on your side.
I would tend to agree that the player had a good point though. It's a matter of flavor in your world. Straight RAW you are 100% right, but I have run an undead heavy campain and allowed for crits from spells that channel positive energy before, balanced things out more. I also allowed for holy weapons to crit, and perform sneak attack though too. But that was because 90% of the badguys were undead and to not allow for the rogues to be useful and for the diferent weapon crit ranges and multipliers to mean something the game would have been unballanced.
I would tend to agree that the player had a good point though. It's a matter of flavor in your world. Straight RAW you are 100% right, but I have run an undead heavy campain and allowed for crits from spells that channel positive energy before, balanced things out more. I also allowed for holy weapons to crit, and perform sneak attack though too. But that was because 90% of the badguys were undead and to not allow for the rogues to be useful and for the diferent weapon crit ranges and multipliers to mean something the game would have been unballanced.