Accelerating the "natural" cycle is bad even if there is no net increase. A massive forest fire technically doesn't cause any net increase in CO2, but releasing that much CO2 at once causes a lot of problems that wouldn't happen if the same amount were released over hundreds of years as those trees died and decayed.
I'm sure some people would argue that burning oil and gas isn't a net increase either, because all of that carbon came from the atmosphere originally. The important question is what emissions will make life worse for humanity, and what can be done to avoid them. Avoidable methane emissions cause real-world problems regardless of their source.
Accelerating the "natural" cycle is bad even if there is no net increase. A massive forest fire technically doesn't cause any net increase in CO2, but releasing that much CO2 at once causes a lot of problems that wouldn't happen if the same amount were released over hundreds of years as those trees died and decayed.
I'm sure some people would argue that burning oil and gas isn't a net increase either, because all of that carbon came from the atmosphere originally. The important question is what emissions will make life worse for humanity, and what can be done to avoid them. Avoidable methane emissions cause real-world problems regardless of their source.