Why does the situation have to be exactly the same?
It doesn't. But to compare two situations that are barely alike except for one common feature, and attempt to use it as a "gotcha!" when you've removed the part of the story that people are actually focusing their comments on is just meaningless. People are commenting on the alcoholism more or less in passing, as it is part of the backdrop to the child abandonment, marrying a woman he didn't love, having more children in this awful situation etc. If you take all of that away and leave only the alcoholism, of course responses would be different. That's really not difficult to understand surely.
For all you know he has been a good husband and father and has kept his feelings buried for 25 years.
Not even going to argue with this nonsense.
In a terrible situation - 2 women pregnant - clearly he had a choice to make
Why? Why did it have to be one child or the other? Why couldn't he have done everything in his power to maintain relationships with both of his children? It would have been messy, granted, but for any decent person it would have been the only way forward. His relationship status should have been secondary to that.
Some things are just indefensible, abandoning your own child being one of them. It's shocking to hear anybody defending this, and even more shocking to hear women presenting this sorry tale as proof that men are victims of sexism. Internalised misogyny is real.