Based on available tools, you can complain we need more methods but you're still without evidence. I mean, we cant do these knock-out and breeding studies on humans. They really do want nazi-tier experiments where we invade lives
 
what available tools are there with any predictive validity aside from twin studies? The other methods I am aware of (like molecular genetics) are inconclusive and nowhere near even having preliminary findings (we will have nothing but small results anyway, nothing holistic)
 
Science is groping for 'less wrong' and 'more predictive' with available tools, not withholding all judgement until an arbitrary threshold is met. This is even dumber because you're doing an appeal to ignorance, saying unless we meet your standard your side is true automatically