It is false because a scientific method is a lot more complex and has many steps which need to be fulfilled for it to be valid. Rationality and common sense are not enough for something to be scientific as sometimes something can be irrational or almost nonsensical and yet scientific.
The unstated assumption in this argument is "don´t eat meat" and if you do it "try to make it in small quantities".
Explanation: having a close look at the sentences, this is what is implicitly assumed-"eating large quantities of red meat is unhealthy" (do not consume meat, it can be harmfull for your health); in fact to be truly healthy, a vegetarian diet is preferable to one that includes meat. (if you really want to be healthy and follow a healthy diet, just concume veggies and get rid of meat).
