Why are these threads so popular? There is no evidence again, as usual.
I think you are mistaking what evidence in this case is. In your case tangible evidence(1) would amount to either kishi directly telling us or something that is DIRECTLY seen in the manga, but a definition like that is flawed in a few ways. On the other hand a looser/better set (2) of rules would be where evidence is determined by the preponderance of the evidence/likelyhood.
Now the issue with the tangible kind of evidence is that it becomes very hard to claim anything as an absolute fact with very few things meeting the criteria. For example, we would all agree that Jiraiya is dead. But in the manga we have seen no burial nor have we seen a dead body but we have seen Kabuto say that he himself could not confirm Jiriayas death because his body was too hard to get to. With that a logical argument could be made that he is not dead, but that wouldnt fit your rules, but also a logical argument could be made that he is dead, but that too requires more proof in regards to your rules. So with this set of rules you can see how hard it can be for someone to assert most things as facts. Which in all honesty is what a theory thread is all about, i mean if there was definite proof of what was being said then there would be no need for making a thread speculating about it.
So then we are left with the 2nd definition which is basically based on the likelyhood being true. Where in Jiraiyas case we can say, "Ok, it may be possible that he is alive and it may be possible that he is still dead but chances are he is dead and based on that likelyhood we are all going to assume he is dead." That is the same logic [Theory] threads go by. There may not be DEFINITE proof (and again if there was there would be no need for making the thread) but based on likelyhood and common sense we can assert certain things as facts or at the very least likely although said thing was not necessarily said to be so in the manga.
