Why so many arguments in Talmud?

Why are there controversies in the Gemara i.e. why did it start?

There are various causes for controversy in the Gemara, which was written after there was no longer a Sanhedrin, so there was no vote taken as to what is the clear decision. In short, among the causes: different ways understandings or deducing from the Mishna; how to resolve between apparently conflicting mishnayot or braitot; different ways of learning from the verses in the Torah; different ways of applying the accepted rules of halacha when conflicting; different ways of thinking; over time- new questions arose and the amoraim differed as to how to apply previous precedents; over time- some traditions were forgotten; originally there were sometimes several legitimate ways of doing things, but eventually the rabbis preferred to have 1 way, but they differed as to which way.