When someone makes claims that something is a "problem", particularly when they start waving the magic word "solution", it's sometimes insightful to replace "problem" with "possible issue" and then ask:

• What evidence has been provided that this is a real issue?
• What is the nature of the issue? Who does it affect, how, and when? Is it likely to affect me?
• How is the issue mitigated?
• Is the cost of the mitigation worth the effort?

In the specific case the visibility of member variables (hash elements) of stock Perl objects, yes, they are visible. Is this a problem? It comes down to a matter of trust. If you trust yourself and your team to not abuse the feature, I'll argue, (based on experience with two substantial perl-based applications, one in the 600KLOC range) that visibility isn't an issue worth the cost of the various workarounds.

If you don't trust your team, then visibility is an issue, but isn't your biggest issue.

YMMV.