Lubavitcher chassidim believe The Rebbe is Moshiach because The Rebbe teaches that The Rebbe is Moshiach. Period and of sentence full stop.
5ish – assuming you are Lubavitch and assuming you are the mentsch you appear to be I am asking this only to you and with full sincerity. Given the above quote of yours, is it therefore hard to understand why someone who is not lubavitch would have a problem with that, given that our Torah sources need always be outside of just a person declaring himself IT?