Unicode is complex because human language is complex. If you want someone to blame, blame God:

> Go to, let us go down, and there confound their language, that they may not understand one another's speech. So the LORD scattered them abroad from thence upon the face of all the earth: and they left off to build the city. Therefore is the name of it called Babel; because the LORD did there confound the language of all the earth: and from thence did the LORD scatter them abroad upon the face of all the earth.

Perhaps attempting to build one character set for all languages is just another Babel-like act of hubris, and the security vulnerabilities are God's judgment upon us for not sticking with the mess of incompatible local encodings that preceded it.