I beg to disagree. There have been alternative explanations for the CMBR.

If the Big Bang has been 'proved', why do there remain dissenters, e.g. the 2005 conference in Portugal?

I'm not sure what you mean by your last comment. That is what seems to be happening over the Big Bang. The majority of scientists/cosmologists believe in it, but there remain a minority of dissenters. They are the opposition, just like in democratic politics.