So, I will answer this as simply as possible…
I see where you're going with the logic you're using, I understand. But it is inherently flawed because it doesn't take into account a few things.
Were everyone a vegetarian/vegan… domesticated livestock would severely decrease in population. The number of cattle/pigs/chickens/etc. on the planet directly correlates to human demand for their flesh and byproducts for consumption.
So let's say people only ate plants. There would not be vast quantities of plants being consumed first by animals then by humans. Therefore, a veg diet is far less land intensive. This leaves land for wild flora and fauna to return to, instead of being used for grazing or growing food for animals. Then, of course, there is water - an increasingly scarce resource. It takes about 450 gallons of water for 1 pound of beef and 20 for 1 pound of wheat (if I remember correctly, feel free to check my numbers).
As for human health… personally I think the health of every creature is important. And as they say, “as above, so below and as below, so above.” So, healthy body… healthy mind. A healthy mind can make better decisions - such as to educate people about overpopulation and the dire effects of a diet with animal products. This new healthy, educated population can then decide how many children they feel is a good idea to have.
And as for the “opinion” part of your statement, I recommend reading a few studies on the long term impact of animal products on the human body. There are also lots of documentaries that might also peak your interest.
All that being said, I'm very glad you asked your question and I hope some other people give you numbers. This is a matter very near to my heart as I haven't eaten meat for nearly 10 years and I let go of all other animal products 2 years ago. Some of the best decisions of my life and I can only hope you ask more questions.
I hope you have a beautiful life.