Here's a hypothetical for your friends who say, "We can't have a trial lawyer in the White House."
Suppose you're sick. Who do you go see? You don't go see just anyone. You go to a medical professional who performs a medical act and you get better. Makes sense.
Now, suppose you are looking to hire someone whose job is to decide which acts of Congress become law. Obvious choice is a legal professional. Someone trained in the law.
Let's review:
Medical Act Required ===> Medical Professional
Decide What Becomes Law ===> Legal Professional