You don't have to slow down everytime there is a newbie on your team, nor do you have to hold their hand, but on the other side of the equation, show compassion and understanding. You have a new person on your team,TEAM. Most of the time if said new person struggles, whole party struggles. It is to your benefit to help new player understand so party can have a smooth run. Especially if you are "grinding" old content because guess what? You are more likely to bump into a new player grinding "old' content that is "new" to them. its not hard people. Stop acting like dicks and just treat people with respect.