Regarding the question "What is a cult?", this can generally be answered 'any group who wishes to abnormally and adversely control people'. I think Steven Hassan's BITE model is one that can assist anyone needing to identify a group as a 'cult' or high mind control.
I have to agree that most, if not all, religions do have cult tendencies, some being definitely worse than others. Cults encompass more that just religious groups. They can be non-religious in nature as well. Again, Steven Hassan has quite a list of groups that qualify on his website.
Regarding Jesus, everything ever written about him came from someone who never met him. The authors of the gospels can't even agree on the accounts of his life. Jesus himself wrote nothing down.
There were a lot of Messiahs back in these ancient times. Did Jesus of Nazareth actually exist? It is possible. But there is no record of this. There is far more physical evidence supporting the existence of the Philistines than Jesus. Bart Ehrman says Paul's letters indicate Jesus existed. Ehrman also says Jesus was an apocalyptic rabi who thought god was going to fix everything in his lifetime. Obviously this did not pan out. Did he walk on water? Did he rise from the dead 3 days later? Was he a man who became a god? No. This is pure fantasy.
