WELL...pre-Darksoul, Katara was pretty much just a random girl to Marco. He wasn't particularly concerned about her, and she was basically just another person to tease.

Post-Darksoul? Yeah, he's not really thinking nice things about her. She didn't just try and stop his mother - she did it in a way that could have done serious, permanent damage. He does know that she was doing it to help, but he thinks she was incredibly reckless about it.

He's also possibly projecting onto her a bit of his own internal guilt over the fact that he wasn't able to keep Eva safe.