The discussion about man parts was in regard to producing heirs. Which is a huge deal for succession and legacy. Danerys claims she cannot have children at all. So that's why it's prominent, not just cus they like men more. Danerys in the past let khal drogo execute her brother in a fairly barbaric way, she torched mirraz the witch lady, she locked varros or whatever his name was in qath in a vault with her previous servant to die a horrible death of suffocation or starvation in total darkness, she nailed a bunch of slave owners to crosses, then she executed a slave guy who rebelled against the harpies, she fed some of the masters to her dragons, she burned tarly and his son, against advice from tyrion. So we have a pretty good history of her being ruthless. Sure many of those people deserved it, but even so the methods, burning mirraz at the steak essentially, melting her brother's face off, burning people. Tyrion and varys saw her burn tarly. That's probably when varys thought oh crap unchecked she's gonna burn innocent people eventually.