What is the objective standard?
Because:
a. Because the people who proclaim this have a vastly different definition of Messiah than "others".
b. Because these people are still Jews in a Jewish country.
c.The Israelis who proclaim this are in the minority of the Chabad movement itself.
For most of world Jewry and much of Chabad the Rebbe contributed great things to advocate following Halacha, making Torah meaningful, teaching people proper values, serving as an example and much more even for non-Jews included. The Rebbe was a great leader for world Jewry. the differences are night and day. The Rebbe never sought to change the Torah and Halachik structure. He strengthened it with all the energy he had at all times bringing thousands of unobservant Jews to higher levels of observance. Far from breaking apart the Torah world, he built it up.
The Rebbe built on the teachings of the previous Rebbe, his father in law, and campaigned to bring Moshiach now. Those followers who wanted him to be more than he was permitted to be, to be the Moshiach, have missed the bigger picture. its hard to lose someone like him, but his teachings and message of yiddishkeit, Torah and doing as many mitzvas as possible as the way to bring Moshiach live on. Chabad has expanded in presence world wide since his passing in 1994 due to his strength of leadership. gimel tamuz (Yartzeit) coming up July 6.
the short answer: the differences are night and day.
Beats me - I'd never heard of the Rebbe until I googled him following your post. Very interesting. Personally I'd say in matters of conscience and religion, people can proclaim anyone they truly believe in - they just have to realise their nieghbours and communities may react angrily. Note, that does not excuse bomb planters - they should be hunted down like any other terrorists. What is the objective standard?
In matters of religion, the only standard is the small voice of your conscience and that is hardly objective. If there were an objective standard, religious wars wouldn't occur and we'd have missed out on some fascinating theological debates...