This prohibition has no biblical foundation, but plays a vital role in separating families, making non-JWs out to be idolaters in the eyes of JWs..
You nailed it FadingAlbatros. That's the name of the game. It's the same with all the crazy teachings about holidays, separate people from their families, friends and entire support system. Then they have to make the JWs their support and can never leave. It's a cult.