[erjiang]

I'm not really sure it's fair to say that people hate PHP because of its flexibility. Many other languages are very "flexible", and much more so than PHP for some things (you're less likely to do dumb threading or malloc mistakes in PHP, for example).

I think it's because PHP has a much larger surface area of questionable decisions to attack. When your core language is very, very small (e.g. Scheme), you have less to criticize, but when PHP has everything and the kitchen sink, plus a lack of an overarching philosophy or standard, plus a broken core developers community, it simply generates many more hatable things.