Because it's a powerful language and during the dot com boom was used by a lot of very poor programmers.

Rails is running into the same problem with overuse/abuse of monkey patching, method_missing etc. that perl ran into with overuse/abuse of rich syntax.

It's sad. But it's really nothing to do with either language. They just handed a large chunk of power to a developer community that grew too large too fast for most of the membership to have learned how to use that power responsibly.

So, do you think the key to Perl 6's success is to avoid that? That is, do you think it's better for Perl 6 to have a smaller, more seasoned developer community in the beginning (to establish some best-practices before the rest of us join in)?

Unless you manage to pull every novice, dabbler, and new developer into the community and teach those best practices from the start, you won't solve the problem on a large scale. Programming -- especially the realm of informal, ad hoc programming so well served by dynamic languages -- rewards individual exploration. You don't have to write elegant Python or Ruby or PHP or Perl to get your job done, and you don't have to learn a lot of theory to accomplish a task. You may make a mess, but it's not clear that novices care about that. Why should they?

Perl 6 has an advantage in that most of the tutorials and examples aren't full of bad examples and muddled thinking like most of the Perl 5 tutorials and examples are. I don't expect that to last, but hopefully some thoughtful language design will make abusing the language much more difficult.

No, the key to Perl 6's success is to convince all of the Perl 5 developers to move on to the new language. Also, if they (the Perl coders) go on a binge and port all the CPAN libraries over to Perl 6, that will help.

To be fair he is talking about the new Perl 6 language. Not the current Perl that everybody uses.

Well quite. Who wants to take over maintenance of a project that's effectively written in the previous developer's personal language?

Perl's not alone here, you can do the same thing with C++ using operator overloading, but Perl actively encourages this to an order of magnitude greater extent.