I'm an inflationary cosmologist/string theorist. I do not typically, or at least not exclusively, think of the big bang as "the beginning" of everything. And my impression is other researchers have that same opinion. Our current physical theories tell us that once upon a time, the universe must have been very very "small" and hot and dense. However, before that time period, we have no idea. Whatever existed before that time probably did not resemble the universe as we know it in any way, so it is the beginning of our universe as we know it in that sense. But the big bang could have erupted within a much larger universe that could have been around forever.