Should chemistry lessons exist? Mixing household chemicals could allow producing poisonous, flammable or explosive chemicals.
Should physics lessons exist? They tell you how to build a catapult.
Should cryptography exist? Only people with something to hide would use it...
... it's a really slippery slope. Restricting knowledge very likely only harms good people, bad people will get the secrets anyways.
Should chemistry lessons exist? Mixing household chemicals could allow producing poisonous, flammable or explosive chemicals.
Should physics lessons exist? They tell you how to build a catapult.
Should cryptography exist? Only people with something to hide would use it...
... it's a really slippery slope. Restricting knowledge very likely only harms good people, bad people will get the secrets anyways.