How much of the IPCC report have you read? If temperatures are allowed to increase 5 or 6 degrees the changes would be catastrophic, even without considering the very real possibility of tipping points triggering run away climate change that would make the planet entirely uninhabitable. There's nothing dogmatic about it, this is our absolute best scientific understanding at this point in time. There are various hypotheses around that allow for the possibility of negative feedbacks that will reduce the likelihood of catastrophe, but so far none have stood up to testing well enough to gain any more than fringe acceptance. I desperately hope somehow one of them turns out to be right, but that's no basis for sensible policy.