If we're going to operate under the law that you should require a license to partake in a complex or dangerous task that could have negative consequences, it would make sense for people to be required by law to be proven relatively financially stable, and emotionally and mentally stable, as well as both parties confirming their consent, before having a child.
This is a nice idea IN THEORY. In practice, like all laws, it's subject to a great deal of corruption.
Are we assuming that the governments idea of financial and mental stability is correct?, the same government allows children to be medicated for psychological diseases they don't have, and has provided consent for torture, lobotomies, and electric shock therapy?.
And remember how finance works, there are many poor parents that would be far more loving parents then rich ones(It's also worth noting that lack of wealth does not equate a lack of happiness or mental health). Not everyone is born into financial stability.
Which leads me to my other point, giving the government control over reproduction opens a lot of doors. What if the government decides that you have to be of a certain background, or a certain career. It's giving them to much power.
In the real world, not all people are created equal. Some are born into privileged families, some are born in gutters. Some are born stronger, healthier, or smarter, some are born with crippling diseases, some are born dead.
This is inescapable. Survival of the fittest, however tragic, is very real. What qualifies as "Fittest" may vary from society to society, but there will always be a ruling class, people who were born into more power, or just got lucky. And none of them are guaranteed to be kind, caring, or responsible.
Humanity's been trading one flawed society for another since the beginning, not by chance, it's our nature to strive, even if it's impossible to succeed, it's what drives us to survive. What reason do we have to believe it will change?
Every law will be exploited eventually, this would be no different. The world will never be perfect, we can't change that, all we can do is survive.