No Stupid Questions

in reference to the fact that you can flip the switch and secure it.

Or ... that's the justification they came up with.

Ever wonder why the 'D' in the logo is a disc, though? ... The "Secure Digital" branding, including the logo, were originally going to be used for an optical disc format that would compete with CD-ROM. With the selling point being the secure part -- DRM-like technologies that would help content distributors do things like region-locking and making it more difficult to copy. They'd already designed the branding and logos and filed for trademarks ... when the project was abandoned. (Likely, they saw CD-ROM dominating the market to such a degree that their competing standard would never take off.) They had invested a substantial amount of money in that branding and trademark, though, so when they started developing the technology we now know as 'SD Cards', they decided to reuse the name, branding, and trademark for this new technology instead.

"Secure Digital" originally meant 'Secure' as in DRM protections. But to make it apply to the next format, they decided to say it referred to the little write-protect switch, like you said.