I think it was obvious they meant the condition of blindness cant't be worse.

No, that's obviously not obvious, since the person you responded to thought otherwise.

"I" think was obvious

And you are wrong, as noted. If you mean "it was obvious to me", that's a different matter ... but it's also irrelevant.

It isn't always pragmatic to account for the 5% of people who misinterpret what is being said or who aren't able to contextualize because they are stupid. We've all misinterpreted obvious things before. It isn't that big of a deal.

But then it's also obvious that this is an irrelevant argument because other things very much can get worse. It's not like becoming blind would be the primary concern of a non-blind person getting a brain implant.

Yes, this is what I meant.

I can imagine some rather catastrophic negative outcomes from novel new brain surgery techniques, even if the blindness were not somehow made worse.