Since entirely deleting modules is impossible (?)

No, it's not impossible - XML::Simpler is no longer on CPAN. If you install modules using CPAN.pm, then it will tell you there is no module by that name in any of the distributions on CPAN. Sure, if you search CPAN in other ways (such as the excellent search.cpan.org then you will find links to modules that no longer exist or have been renamed - but that problem is hardly limited to XML::Simpler.

Perhaps you could come up with [...snip...] a "tutorial module" ...

As it happens, I have 'come up with' the Perl XML FAQ. As time permits, I intend to expand the concept into a CPAN distribution XML::FAQ which includes lots of sample code.

two problems that plagued me were 1. killing the parser with bad input...

Covered here.

... and 2. getting back a different character encoding than was input

Covered here.