Nevertheless, if there's a MANDATORY evacuation order, and the mayor is out there basically telling people that they're going to die if they don't find shelter somewhere, and you decide "oh, it's not really that bad," then yeah I blame you when you end up on your roof.
The folks who followed instructions and went to the Superdome are blameless. The folks who couldn't get to the Superdome but had the werewithal to get to the Convention Center are blameless. The folks who were too old, too weak, too sick, or had too many people under their care to evacuate are blameless.
Take all those people out of the equation, and you're probably down to just a few thousands of people whose predicament is just because of their own stupidity. And of those, a significant portion are just savage criminals who wanted to stay behind so they could prey on other victims.