That is true, so the pieces of meat which were placed on earth by god 6k years ago can be eaten guilt-free. However, all other pieces of meat require harvesting from an animal first, incurring the aforementioned downsides. Just as purchasing an item encourages its production, eating meat encourages its purchase.
Here are two simple scenarios where eating the meat does indeed cause meat to be produced:
- your eating it means that another person doesn't eat it, so another piece of meat must be purchased for that other person;
- your eating the meat signals to whoever got the meat for you (perhaps yourself) that you are willing to eat meat and hence they pick up a propensity to get meat for you again in the future.
Isn't this simple common sense though? Were you really not aware this is how the world works?