Some soy is fine, but if we're talking as completely replacing your meat, it could be too much estrogen like compounds. Hence breasts in men and an increased risk of breast cancer in women. I haven't seen enough studies to definitively rule these out.
Besides, variety is always good. It's never wise to put all your eggs in a single basket.
Besides, variety is always good. It's never wise to put all your eggs in a single basket.