Could you explain then why B::DeObfuscate is usefull for *non-obfuscated* code? Obviously there is no use in running it over non-obfuscated code. So the sole purpose of it is making studying obfuscated code simpler.

I never said is was useful for non-obfu code. I said:

It's a generic deobfuscator, not specific to Perl-Obfus.

Making obfuscated code easier to understand is not illegal, unless it contradicts the licence agreement you have the code under.

Writing code to de-obfuscate code is not illegal full stop.