Technically <em>true</em> as far as the statement goes, but the statement is deceptively general.
Carbon Dioxide is a greenhouse gas, and is essential to support plant life on Earth.
But there's such a thing as "Too much of a good thing".
Water is essential to support life on Earth, but too much of it can drown life.
Similarly, Carbon Dioxide is essential to support plant life, but too much of it would make the Earthly environment hostile to plant AND animal life.
Which is the direction in which the Earthly environment is heading now.
