Capturing the King should be legal. This leads to general softness

If someone doesn't see that their King is in check, they deserve to lose their King, and they deserve to be ashamed. 

To make a move that leaves the K en prise should be legal.

The rule against this is overprotective of the egos of beginners and any real chess warriors.

Real men play without this protection.  Chess must be returned back to its origins, where men fought for blood.

This will be important in the nearing apocalypse! 

Keep up the strength of the warriors of planet Earth: do away with this overprotective rule.

In case this opinion is not unanimous, chess.com can make it an optional feature.

Hear, hear Cavatine.  You are wise.

It'll never happen, so go away.

No, castling rules would be simple, assuming only the OP's rule change would be put into place, they all work in spite of any check threats. Checkmate would not exist, check would only be a simple notice, if that, the actual goal of chess would be to capture the King. Since a king may move even if it would be attacked, the act of checkmating is only a one move lock. Stalemates would not exist, since a king can legally move and die, this would be a win for the player who locked the king. Draws by insufficient material are also eliminated, as a king may win the game by taking an opposing king that moved next to it. That said, I imagine certain policies would be changed if that rule change actually occurred, as certain things start looking very ridiculous.

Despite this being what seems to be a troll thread, this is something I suspect many players wonder about, especially newer ones, (I know I certainly did, after all, isn't it obvious to move your king away from an attack? Why make it a mandatory action for something that would be stupid to miss?) Once you start looking at the way the rule change affects other aspects of the game, the reasoning starts making a lot more sense.