I used to be a Catholic. I left because I object to conversion by concussion. If you don’t agree with what they teach, you get clobbered over the head until you do. All that does is change the shape of the head.

Alda uses comic exaggeration (“conversion by concussion”) to criticize coercive or punitive approaches to belief. The line suggests that forced assent—whether through intimidation, social pressure, or literal violence—does not produce genuine conviction or understanding; it merely compels outward compliance. The punchline (“change the shape of the head”) underscores the difference between internal persuasion and external force: you can injure or silence someone, but you cannot meaningfully change their mind that way. More broadly, the quote reflects a humanistic preference for dialogue, empathy, and reasoned argument over authoritarian certainty in matters of faith and ideology.