My thinking is that one of the attractions of Debian is the superb packaging system - that's one reason I got involved with Debian to learn that packaging system. Almost every change one might want to make to a system could be made via the packaging system. That then gives reproducibility and possibly, when combined with local netinstalls and repositories, scale. However this implies that on some *production* machines one would logically want to remove CPAN and CPANPLUS in particular and development tools in general. One does not want one's nice apt based site management system undermined by users being able to break system wide policies.
I would not pretend to argue that on the scale of security issues, this is a biggie. Rather I feel it is more of an issue about bing able to have confidence in how one's systems are managed.
I'd much rather see a solution where the Perl core (aside from perl-base) is split into small binary packages so that package dependencies can be declared with finer granularity and the installation footprint cost of using standard library functions is lower.