The Brazilian forward appeared to headbutt Motta in the tunnel after PSG's 2-0 win over Bastia in Ligue 1 on Saturday.
PSG president Nasser Al-Khelaifi has called for Brandao to be banned for life after the post-game incident.
David Luiz said players had a responsibility to set a good example for kids and Brandao had failed in his duty.
"We have a great job in the world to show a good example inside and outside the pitch. I think many kids in the world want to be us so they know about everything," he said.
"That is not part of football. I don't agree with this.
"Sometimes on the pitch you are more vulnerable with something and they speak bad things, but that's normal in football.
"But when you wait for someone outside the pitch to do a bad thing. I think that's not [acceptable]. That's not part of football.
"So I'm not happy with this because after that everyone in the world knows about this and like I told you that's so important when you give a nice example for the kids."
