How do we get from “we know which mountain was Mt. Sinai” to “the Exodus did happen?” I did not bring up Mt. Sinai, another poster suggested that it would somehow be informative.
The evidence against the Exodus is that archaeology has found that early Israelite settlements were basically identical to Canaanite settlements. Their pottery, alphabet, and even gods initially match indigenous Canaanite settlements. This strongly suggests that there was no sudden arrival of migrants who had lived in Egypt for a few hundred years, but that the Israelite people were actually locals. Moreover, it is essentially impossible to match archaeological evidence from Egypt to archaeological evidence from Canaan. Basically, there is no evidence that a large group of people was expelled from Egypt around the same time that a bunch of Canaanite cities were destroyed.