Should the manufacturer of the camera be held responsible because they did not verify the purpose of the buyer and consequently allowing them to produce illegal material? (They could technically have some online DRM installed to all of their cameras and if it is reported that someone is making illegal material, they can brick those cameras in question.)

I think the issue is that Visa should not be tasked with enforcing the law. In my opinion, in an ideal world, PornHub should be forced to verify its content not by Visa, but by the government, i.e. there will be heavy fine for allowing illegal materials to be uploaded.