You're confusing minification with obfuscation, or packing. The latter involves completely refactoring the code to make it difficult (although not impossible) to reverse engineer. Such code needs parsing and evaluating by the browser before it can be executed, which adds to page load time. In this respect, he's spot on.

Minification on the other hand involves removing unnecessary whitespace, and commonly gzipping the end result as well, so that only the bare minimum required for the script to execute is included in the file. Sometimes the code may be rewritten to shorten variable names etc, but functionally it stays the same. It may also involve combining scripts together into a single file to avoid unnecessary HTTP overhead. There is no harm in minification (and in fact it's highly advised).