That's the sound of the key point whizzing past you, as you trot out a trite and unhelpful sound-bite.
(Unless, of course, you want to argue that it is only to be expected that the designers of power nailers refused to acknowlege that it could be used to nail yourself - until after someone demonstrated that you could nail a person. Because the C++ template designers did refuse to acknowledge their creation was Turing complete until someone rubbed their faces in it)
Who cares?
What difference does it make if the "C++ template designers" weren't perfect engineers. Who cares if they didn't set out to build a
Turing-complete meta language, but discovered one along the way? Heck, I bet they suffered from bad breath and questionable politics too, but that doesn't affect the utility of what they created.
Sometimes useful things are discovered rather than conceived. Like
Penicillin, for example, or
Teflon. You know, Astroglide was an
accidental discovery too.
C++ is like Astroglide for programmers and I, for one, will not be going back to life without it.