Larry, I think you're taking the "shouldn't" too literally. I do believe he meant in a more light-hearted tone.
Not that you shouldn't because someone made a rule, but shouldn't in that it's not part of your normal pattern, or normal habits, or normal definitions of what you tend to like.
For example, Larry, I am pretty sure you're not a metalhead and don't normally listen to anything even resembling extreme metal. Thus, listening to metal, in your mind, is something you don't do, and if a new metal band came along, you more than likely shouldn't like it based on your established habits and established likes.
Now if you suddenly fell in love with Jinjer, a metal band from Ukraine, and suddenly felt compelled to buy their albums and go see them live; no one is going to say you shouldn't because you are not allowed. But it would be out of character for you, thus, you shouldn't like it based on past likes and dislikes.
When I was teen, I had this thing I wouldn't listen to bands who used a drum machine, I would only listen to bands who had a real drummer. Hey, it was the 80's, what can I say.Then at 18, I was introduced to a band called Clan of Xymox. I fell in love with them. They used a drum machine. I shouldn't like them based on my listening habits and rules in my head at the time. But I did (and still do). I had to eventually realize it was a dumb rule.