> Another is that if taking paternity leave impacts men's careers, then in many cases both parents will suffer such an impact...
As the article states: how are these factors different for men than for women?
For the sake of this argument, they aren't. It's not about which gender they impact. It's about what percentage of relationship participants they impact.
Right now ~50% of relationship partners face credible career setbacks as a result of post-childbirth leave. Changing that percentage to 100% is probably going to have some ripples.
That's not to say it might not be worthwhile, just that it's unlikely to be as simple as "flip a switch, everybody acts the same".
The he whole point is to eliminate one of the primary causes of gender inequality in the workplace. Spreading the burden of parenting is exactly the right thing to do.