Who cares if it's been warmer before or if it would warm (albeit much more slowly) anyway due to natural causes. The fact is, we know the warming is driven by greenhouse gases and while there are some of these occurring naturally we are certainly making things much worse. Your arguments are no reason not to take a aggressive stance on cutting carbon emissions.

Put another way, the real question is not are we causing it but can we slow or stop it by making changes. And the answer to that is undeniably yes.

As to the argument that the earth survived warm periods a thousand years ago so it's no big deal - are you kidding? There are billions more people alive today, and probably hundreds of millions in places that will be affected by sea level rise or droughts, not to mention the economic impact of other extreme weather events.