Read the original question again. The OP was specifically asking about shared hosting environments, and it's specifically in such an environment that there are the security issues I mentioned. In such an environment my suexec'd FastCGI backend can't muck with your suexec'd FastCGI backend.

And I wasn't talking about modifying global configuration, I was talking about modifying code. If your site ran CGIs under Apache::Registry and I can divine the generated namespace your site's handler gets compiled to I can write my own CGI which shims code into your site's namespace in place of yours. Or I could override DBI::connect with my own version that writes off your database credentials somewhere. Or I could override CORE::open and . . . well, one sees where that's going I hope. That there's no easily configured and lightweight (relatively speaking) way to sandbox mod_perl is the deal killer for shared hosting that the OP desires.