It too complex, hence is justified to say incorrect to analyse it on such a simplified level. While carbon dioxide is essential for life as a fundamental component of the carbon cycle and a necessary greenhouse gas, it's not a simple proxy for the health of life on Earth. High levels of CO2 can be detrimental, leading to environmental disruption and negative health effects, making the relationship extremely complex. It is safer to say it is not because it will make you to dig deeper and to find out more than just that ambiguous and catchy phrase. Have a look for example how some employers keep employees suitably anxious to increase productivity using higher carbon dioxide levels in premises. It's very complex, mate, and that example shows how levels range makes difference.