Earlier quoted context omitted.
>the verb 'to entitle' is a strange one in that it is often tricky to pin down what would be the subject of an active sentence using entitle as a verb. It isn't difficult at all. E.g. in "This coupon entitles them to cheese", "this coupon" is clearly the subject. You may be thinking about thematic structure more than grammatical relations.
So—if I am entitled, what is doing the entitling? You rewrote the word as active which I guess is a valid point but a complete departure from conversation and not at all in good faith, my friend.
We also seem to use "entitled" to mean that someone thinks they are owed things when they aren't - you often find this in rants about individual jerks or millennials in general. There's no subject to be had in that use because the entire point is that it is not legitimate.
I think the latter sense is always an adjective. The former sense clearly can be a transitive verb, and I have not found a seemingly grammatical utterance that can't be described that way (I think - IANALinguist). The fact that the subject can be left unspecified is a feature of the passive construction in general, and an often-stated motivation for some of the criticism it receives.