Six missed reasons for a counterattack

In my last club championship game, I had Black and in the 11th move of an English opening we came to this position.



Black to move.

My center pawn is attacked, and this post is about why on earth I played a weak move (c5) to protect it.

1. The first and most important feature of the position is the uncastled white King. He needs a full three moves to castle. This alone would have been enough compensation to give a pawn.
2. I do not even give my pawn but gain it back with my counterattack d6-d5.
3. My e-file is already half open to the opponent King.
4. The Knight, grabbing the pawn, exposes the King.
5. After having taken the pawn, the Knight is unprotected.
6. With my counterattack d5xc4 or d5xe4, I launch a discovered attack on the unprotected Knight.

Yeah, instead of «oops, my pawn is attacked, I must protect it» I should have looked at the whole position. Even the simple rule «checks, captures, threats» would have done the job. By the way, after my weak move, the position was dead drawn and I, trying to force a win, ran into a counterattack and lost.