I remember when the theory was first presented. There is ample evidence of global glaciation in the distant past, so i personally have never had a problem with it. Of course the one big issue is the world was a water world for the vast majority of its time. The first continent UR, was smaller than Australia and formed about 3 billion years ago. For the next two billion years not much happened on the continent forming front until UR merged with NENA and ATLANTICA to form RODINIA.
That first super continent was it, and it wasn't all that big, so yeah, a global flood is not just likely, it was a fact. Only it wasn't a flood, it simply was there wasn't a lot of land to erode in the first place. Interestingly though, there are parts of UR that still remain, they are found incorporated into India, Africa, and Australia. There is a theory that a continent existed before UR, but there is no evidence for its existence that i know of.
So, "Snowball Earth" is not really a stretch knowing what we know about the climate changes that the Earth has undergone.
