Yeah, I have a couple of thoughts about that, as a new parent myself (baby is 11 weeks old). Granted, for places that offer paid leave, it must seem like a free vacation to some. But paid leave for a new child isn't exactly a vacation. It is mostly an exhausting and stressful period of time, as well as one that is of critical importance to the development of the child. Honestly, I'm generally more worn out each day than I was when I was in grad school.
I do, however, agree that non-parents can get the shaft in a number of ways for time off, and that paid leave does amount to an added "perk" for those that choose to have kids. As a compromise, I would settle for a much higher minimum standard on annual vacation, say from 6-8 weeks somewhere. Then, a simple rule: you can use up to 26 weeks (6 months) of vacation time for family leave whether you have it accumulated yet or not. If you don't have it accumulated, you go negative, and will owe your employer that amount of pay when you separate if you don't accumulate back up to 0. A brand new employee might be hesitant to take all 26 weeks for fear of owing a ton of money in the event of a separation, but a "forgiveness" could be made in the event of a forced layoff or something. To reduce negative hours for newer staff, you could also use a shorter term, or stipulate lower pay. Example: give yourself half pay for 16 weeks and use only 8 weeks of vacation, which will be made up within 2 years easily assuming you start with 0 accumulated. You can still charge vacation hours while you are making up your time, but are limited to 1 week per year until you get back up to zero. It would skew the benefit towards more senior staff, but would still be hugely better than what most people currently get.
Aside: I got my 12 weeks of FMLA, but it was unpaid unless I used vacation time, which I only accumulate 2 weeks of per year and didn't have anywhere close to enough of. I'm the dad, so it was back to work for me. But my wife just quit her job, which also gave a whole heaping 0 weeks of paid leave. You want to know where the "gender gap" comes from in the workplace payscales? Look no further than interrupted careers due to childrearing, due to the fact that you can't get any paid leave but yet still need to raise a child. Then people look at you funny and lowball your salary when you come looking for a job again a year later because you have a "blank spot" on your resume.