I don't think the implication is that the Earth won't recover from our climate change issues (it will, we won't). So saying there was lots of life in the Cretaceous period doesn't really make sense, since I could also say there was plenty of life when organisms only existed in the sea. That doesn't exactly help our survival as a species, does it?

It's also not about whether temperatures at this exact moment are higher or lower, but the trends and the rate at which those temperatures are changing. If we're looking at the graph (I'm using [1] linked below for reference), and in 1000BC it was warmer by 2-4°F, but the slope of the graph is way less pronounced than it is now, that's not exactly reassuring.

[1] - http://www.longrangeweather.com/global_temperatures.htm NOTE: I'm just using this graph to visualize the trends, and since it doesn't provide exact numbers on the axes I'm just looking at the overall shape of the graph.