Time off to have a baby could be considered a right.
I'm not so sure being paid for your job while you are not working because you have had a baby is really a right. It's a policy, and not an unreasonable one, but that isn't the same thing. Because that would mean it's an intrinsic duty of others to pay for the costs associated with being a parent. Notably here the employer.
We make policy decisions all the time about what costs related to parenthood are best shouldered by society as a whole, or by individual families, and it's a balance. No one says society should pay for everything. OTOH, not only does helping with things like education help society as a whole, you can make a very strong argument that society benefits from people having children so we should all contribute to their care, even (maybe especially) those with no children at all.
But there is a lot of room also to think about other effects policies to support families or mothers or children will have. One of those things is what is in fact fair to others to have them contribute. Taxes are taken from other people and there is a question of fairness around what levels are reasonable.
The question in this case around the impact of the policy on employers is an important one. Both monetarily and in terms of having an employee out for a long period which can be a problem in itself and maybe is in fact the more serious issue for many. If the burden is serious enough that it's regularly a problem for smaller businesses, that's not irrelevant just because we invoke women's rights. People do have a right to be able to make a go of a business, and it's good for society and the economy. We shouldn't be happy to have a situation where smaller businesses or entrepreneurs are not able to function because of the policies around any kind of employee support, unless we are happy to turn the entire economy over to big business.
If that is the case maybe there needs to be some serious thinking about other solutions.
Now, maybe this isn't really that big a problem, that is a fair response. But saying it can't be discussed, there is no balancing of goods here, and "if you believe in women's rights you can't even think about this" is one of the worst trends in politics that means we have bad policies that will inevitably lead to shitty results, because anyone who questions their efficacy overall is branded some kind of nasty person.