Careful v Carefree. From a purely english gramatical sense, these words have almost the exact opposite meaning.
From the Oxford English dictionary,
Careful - • adjective 1 taking care to avoid mishap or harm; cautious. 2 (careful with) prudent in the use of. 3 done with or showing thought and attention.
Carefree - • adjective free from anxiety or responsibility.
I must admit I've really had a laugh at Bill Gates statement from your link,
For years, in the interest of the overall health of the computer industry, we permitted the free and unfettered use of our proprietary numeric systems
Classic
I think even George Boole would have probably seen the funny side.