Hockey is an extremely fast game where often everything happens in literally milliseocnds. When you're about to hit someone in a situation like this and it happens so fast that you can't even process the thought in your head before you're about to hit them, then you're operating on instinct. Namely what comes naturally to you which in that situation is probably to raise your arms and to brace for an impact with another player.
The problem is these rules don't care about any event leading up to the hit (player was bracing himself for a hit to prevent injury to himself and unfortunately the collision resulted in injury to the other player), they just care about the result (hit to the head). There needs to be context just like a person who goes on trial for murder can often have a justified reason for killing someone like they were fighting for their life etc. rather than saying 'You murdered someone and it doesn't matter that you were fighting for your life, you're going to prison for life'.