I have finally read through this entire thread and would like to add/clarify a few things. I hope it is coherent enough and not to disorganized... First I would like to further emphasize the distinction some have tried to make between hate and strong disagreement and disapproval of a certain ideology. While there are always people who will turn a purely shem shamayin ideeoligical battle into a hateful immature fight that does not discredit the ones who are sincere about their belief in the ideology being wrong yet love those who believe in it because they are Jews. It is perfectly understandable that someone from the lubavitch perspective will have strong emotional dislike and intellectual disagreement for what Rav Shach said. On the other hand, from an intellectual viewpoint can you understand that a gadol can feel that there are people who have views and haskafas that are counter to Torah haskafah yet they are being confused as acceptable positions. The gadol therefore feels he needs to take a very strong stance to counter this perceived negative influence. The gadol also feels that there is a person who is responsible for it and he must be discredited lshem shamayim? (i am not saying it is right in this case nor whether you should agree, nor that you shouldn't be upset about it, I am just saying it is possible for a such a position to exist about something and if a gadol feels it is true that it makes sense that he would act that way and not God forbid be a rasha). To say that the Rebbe would never do such thing seems a little funny-why not? If he felt that a different segment of Judaism was leading people down the wrong path shouldn't he come out very strongly and do what is necessary to stop distance it from his understanding of acceptable torah hashkafa?
Second, Dan is correct in stating that the strong disagreement (liberal substitute for hate- see my first point) existed before messianism. However, it is the same issue that many gedolim were concerned about in the Lubavitch movement that they believe manifested itself in Messianism. As an illustration (not proof) of this point, someone said earlier (don't remember who I am not going to go back through all the pages to find out) that you see many chassidim going to the Rebbe but you will never see a lubavitcher go to another Rebbe for a bracha. This was said as a positive thing but from an "anti-lubavitch" perspective this type of attitude is viewed as very scary and dangerous. There have always been many factions within Judaism but Jews from each faction always were machshiv the Gedolim from other factions and considered the various gedolim equal or sometimes even greater than their rebbe, rav etc... even if they were not their mesora and certainly worthy of getting a bracha from. Maybe there was a specific disagreement to a particular gadul, never all of the other gedolim. Correct me if Im wrong but that doesn't seem to be true with lubovitch. They seem to have held that no one is comparable to the Rebbe at all. This was not the only issue they have with lubabvitch. I am not well versed enough or qualified enough to go into all of them I am just trying to explain why that same "disagreement was there before hand".
Another point I wanted to make is regarding this line that many keep saying about it mashiach being someone who is dead as being within the guidelines of shulchan aruch. I am no expert in this area of halacha by any means but am I correct that this is not the mainstream halachik view? Assuming I am correct there are many minority shitas all over the place in Torah and halacha, in general we follow the mainstream, accepted halacha unless there is a mesora otherwise. I can't imagine there has been a mesora passed down in lubavitch that they hold mashiach can come from the dead (again corecct me if I am wrong, but that would be really interesting). So if it is not from mesora where does it come from to place such a strong belief in and emphasis on obscure non mainstream shitas ( i believe this particual point may be similar to the issue that many have with slifkin).
