If every class in the game was hybrid, I would be ok with this, but they're not. It would be unfair to allow them to swap between different roles on the fly, when other classes are regulated to one.
Why?
So I can't go from solo'ing DPS merc to healing merc because some classes like the sniper only have DPS trees? At the moment my respecs have hit 25k~ and that's just from respecing every other day to heal for friends in Flashpoints. Such a fucking ridiculous system.