Isn’t he divorced?
Indeed, but he was married until recently. And his son will always be his son.
I’m sure they are going through a rough time. Nothing here is about them. I think it’s perfectly in line to express shock indignation and outrage about what he did, and it shouldn’t make it more painful to them that people think so.
חפץ חיים כלל י ד
שיתרחקו הבריות מדרך רשע כשישמעו שאנשים מגנים פועלי און
I'm not saying that it's not normal or allowed. I'm saying that it can have negative implications for victims.
Imagine his son, now 12-years-old, and being at least somewhat in the dark about what went on. He gets a little older and comes across the Daily Beast article or is told by others about his biological father's antics. He's shocked and embarrassed, but he can save face by convincing himself that none of his friends read it and that the frum community doesn't know of his father's actions. But when a quick Google search brings up DDF and he sees that everyone in the frum community hashed out every aspect of his father's infidelity, he may forever walk around with a stigma on him.
Not saying I would've thought to consider this if it would've been a random stranger. Perhaps it is a fault in me. But since I know them, and I know how upstanding and innocent they are, this consideration bothers me.