1. module writing is about avoiding namespace clashing
2. the proper use of globals in modules is the same as perl does with builtins like map and grep - aliasing them
3. having $_ blown away is learning the hard way how to use globals properly: not to trust them once you give away control over them
4. $_ isn't really a global, but a default - think scratchpad
5. for really real global values everywhere, there is ${^_My_Real_Global_Var} - the "^_x" thingy (see perlvar at the end)

So it's all about intent - if you inadvertently overwrite $_ or inadvertently get your $_ overwritten, it's fault in either way. If you do it deliberately, you'll do it (at best) for educational purposes - "hey, I wiped our scratchpad, isn't that nice? fix your code" :-)

Anyways, I personally think $_ and friends should be seen as belonging to no namespace but the CORE, and closer to the default main namespace.

--shmem

<update> - added curlies for My_Real_Global_Var - thanks Hue-Bond </update>

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}