That is what some astronomers say, the earth's natural wobble would be much greater without the moon, so great that there wouldn't be a stable climate zone for lifeforms to find their niches. Maybe so. One of the outer planets is spinning so far over on its axis that the seasons are as radical as possible. Summer at the pole lasts for years with the sun way overhead. Then winter with no sun for more years. If earth did that the arctic would boil dry and the antarctic likewise. Not life friendly.
The Toba volcanoe almost wiped out homo sapiens once already.
After the eruption 73,000 years ago, the human population dropped drastically and reached a bottleneck population of about 1,000 people (the bare minimum needed to sustain the species in a healthy fashion.)
This bottleneck is also responsible for the lack of genetic diversity in us. Compared to other species we are one of the most similar genetically.
Toba played a big part in that.