I think a major part of the problem here is that the DM is allowing it to happen within his own HR. RAW specifically states under the spell description that if the spell is evoked in a creatures space, they take damage as though they had passed through it, IF they fail a reflex save, which would negate the damage entirely via avoidance and moves to a space of their choice on either side of the wall.
"An immobile, vertical curtain of whirling blades shaped of pure force springs into existence. Any creature passing through the wall takes 1d6 points of damage per caster level (maximum 15d6), with a Reflex save for half damage.
If you evoke the barrier so that it appears where creatures are, each creature takes damage as if passing through the wall. Each such creature can avoid the wall (ending up on the side of its choice) and thus take no damage by making a successful Reflex save.
A blade barrier provides cover (+4 bonus to AC, +2 bonus on Reflex saves) against attacks made through it."
The issue always arises when using out of game logic in an RPG setting. If you start going down that road, there are certain spells that will absolutely dominate and make savvy caster power gamers run the game. I would just use the rules already in place for it, the reflex save. If the player wants to take Spell Focus, GSF and the like to make it harder to avoid, that's his choice but not using the reflex save like that removes the purpose of those feats and creates unbalance. If I am misunderstanding the problem, please let me know.