Well, there's a difference between being and acting. This typical attitude seems to be 'fake it till you make it' spirituality.
There is another way to read that passage. The word must could indicate either compulsion (as in: you must do this or I'll smack you upside the head) or must as in certainty. (this MUST be true, how can it not be?) If you read that passage in the second sense of the word, the thought becomes: "Of course you're perfect, after all, your heavenly father is perfect."
To imitate is not being, it is pretending. All this stuff is supposed to be by God's grace even according to traditional Christianity right, but here are some clowns thinking they got a nice system whereby you can put in so much works (in the case of JWs, actually counting the hours) to rack up some brownie points, like slipping God a few bills to get a good seat in Heaven/Paradise or whatever. Well, I will just say this: If you only had a different idea (or no idea, actually) of love and what it means to be perfect, (which of course goes hand in hand) the understanding of that scripture can change completely.
When is a good time to introduce the idea that maybe the different ideas of/about God in the bible are not the real thing? Most of the time it's "this idea contradicts that one" - but what about just all of them being ideas period? All thoughts, all the same class of things - concepts. You don't have to get upset at the thoughts, they are just thoughts. Just see it for what it is, it's not like any concepts are going to be the real thing anyways, that's why they're called concepts.