Water is not a poison... it is essential for life.
But you can drown, a tidal wave can destroy property... Really there's many mechanisms where water can do damage.
Similarly, there's many mechanisms where CO2 can do damage. You just choose to remain ignorant of them.
For example - while humans can survive CO2 concentrations of 1000ppm like you mentioned, when it's that high it impacts the ability of children to form new memories.
You just aren't qualified to make a call on what percentage is important. You don't even know what calculations to start with. Your reasoning is just based on mudguts feel, not logic.
