No red card awarded if a player makes a genuine attempt to play the ball as a penalty is deemed punishment enough.
Perhaps so... but in this case, the rules failed to restore equity. There's virtually no chance that Croatia would have failed to score; meanwhile the defender is attempting to win the ball from behind the attacker lunging in in desperation, bringing the attacker down as a foreseeable consequence of the tackle.
What turns this into a red? Must some sort of injury occur?
In this case:
1) It was a foul;
2) It was from behind;
3) It was a slide tackle;
4) The attacker went down;
5) Clearly, the attacker might have been injured as a result.
To me, this is a still a clear cut red.
Unfortunately, the rules are too subjective IMO - so that reasonable people may side on either side of the red-or-not debate here.
========
To be clear, I think that a red should have been awarded - if using player safety as a reason, then yes.
Why? Equity was not restored. Croatia were robbed of a goal - and more importantly could easily have lost the match.
Slide tackling from behind as a last man trying to win the ball? - OK - but if you commit a foul, it's got to be a red. (Yes this might not be how the rules are currently written but it's how I'd rule on the field given the current rules, citing player safety to get my way. IMO, the rules need to be adjusted here for several reasons:
1) Equity was not restored;
2) Dangerous tackles are encouraged.