The people complaining about “key magic ruins everything” should slow down and think really hard about what Key stories would be like if they were strictly realistic and did not utilize Key magic.
Angel Beats wouldn’t even exist. And all other key works would be just ‘stories where some characters die in the end for no good reason’ instead of ‘unrealistic stories where all problems are magically resolved’. That’s hardly the better alternative. Why? Because the death of certain characters would destroy the meaning of a key story and change its central topic.
Just try to imagine the consequences of Key magic not happening in Clannad. Could it still be called a story about family?
For me, key magic is a form of justice in the universe of every key story. Life is harsh, nobody’s denying that. Any kind of tragedy might strike you or the people close to you at any time. Effort doesn’t always pay off. Dedication doesn’t always pay off. There are no guarantees, no matter how hard you try or how much you struggle. All you can do is somehow come to terms with whatever happens and move on.
But even if life betrays you, key magic will not. If you always give your best, if you treat your loved ones with utmost affection and support them the best you can, if you never give up, if you keep fighting no matter what happens and give it your all, key magic will grant you the happiness you deserve.
As a tool, key magic enables the author to let the readers experience the most extreme sadness, despair and happiness. He can create irreversible tragedies, then still turn them around. It adds another giant loop to the emotional rollercoaster that makes key stories so impactful. And personally, I prefer feels over realism.