[arrowsmith]

"systems can become corrupted (or simply fail) and no longer work towards their original purpose"

Er, that's exactly what "the purpose of a system is what it does" means.

[chongli]

No, “the purpose of a system is what it does” implies that the original intent of the creators of a system was for it to become corrupted.

[arrowsmith]

That's one way to read the literal meaning of the words, but it's not what the phrase means as originally intended.

[chongli]

Right, but then we apply the phrase to itself and this is what we get!