In perl, Regexp matches are used to do a lot of different things, and removing malicious characters is only one of them. So for perl to assume that a variable derived from a tainted variable through a regexp match is "clean" is dangerous.

No. You have that backwards. Perl is not "assuming" anything. Perl is not a living entity. It does not make assumptions; nor can it take circumstances into account.

Perl gives you a simple mechanism, which you can either use correctly; or not.

It is like speed limits. They may be set at 70mph (or whatever prevails in your part of the world), but that does not absolve you from responsibility.

If you try and drive your car at 70 in torrential driving rain; thick fog; or when there is likely to be black ice about; don't go blaming the result on the speed limit.

See what I wrote here...

So, you wrote a bunch of code without considering security; and now you want to 'fix' Perl; rather than fix your own code.

I have no say or influence in these matters; but it is a pretty safe bet to assume that Perl tainting isn't going to change any time soon, so you'd best expend your effort fixing your code.