Faced with incontrovertible evidence that Jack was his son, Ryan was unwilling to harm him. Even though his child was designed to kill him, built for that goal, Ryan stopped short.
Lamb was willing to suffocate her child as she slept to attack someone. Her child was a means to an end, conceived for her ultimate goal, not by a malign conspiracy but by Lamb herself.
I don't think, given the player's perspective with relation to the children, one needs to employ misogyny to explain why most people consider one more evil than the other.
Aside from the children, they were both incredibly evil people. But where Andrew Ryan was driven to his most atrocious extremes by the implacable manipulations of an external force, the evils that Lamb performed were part and parcel of her plan. She had no adversary that pushed her to manipulate, to deceive, to destroy until the last day or so of her reign. Other than Delta, her greatest enemy was the people themselves -- their hopes, their desires, their ambitions.
Even so, each was willing and able to commit atrocities. While one might be more sympathetic towards Ryan, the reality is that both were incredibly evil.