What argument is that? You don't have any possible justification for choosing PHP. Ask anyone with more than a few months' exposure to computer programming.
With Python (as just one example), if I am a student, I can run the language in a bare-bones text terminal and get useful results and feedback. I cannot do this with PHP.
With Python, I can start an interactive, graphic session to get immediate, instant feedback in my experiments (IPython and others). I cannot do this with PHP.
With Python, if I happen to be underprivileged and want to learn programming, I can support my efforts with a simple computer with few resources and no HTTP server running -- like a Paspberry Pi. I cannot do this with PHP:
http://www.raspberrypi.org/archives/tag/python
If I make a syntax error, I get immediate feedback, with a description and a line number. I cannot do this with PHP.
If I want to learn object-oriented principles, Python and Ruby both support full-fledged classes. PHP's support for object-oriented programming is, like everything else, a weak substitute.
It isn't possible to imagine a worse choice for students. In fact, I just realized you're not serious -- you're trolling. You want to have a pointless discussion about a crippled language.
> Why don't YOU write your own book using whatever language you want ...
As a matter of fact, I have written several languages in my 40-year career, and I was programming before you were born.
PHP is not a general-purpose computer programming language, it is a dedicated tool for designing server-side content, and it possesses a number of serious drawbacks. Teaching programming with PHP is like teaching mathematics with an abacus.
And if you were qualified to have this conversation, you would already know this.