In an ideal world every child would be planned and it's parents would have sufficient money to provide for all it's needs. The real world is far from ideal, unfortunately. People have unplanned pregnancies, marriages break down, jobs get lost and so on. The jury's out on why people have babies, but the fact is that they do regardless of whether they can guarantee to meet the child's needs.
But in UK 2018 we have extremely reliable methods of contraception if used as per manufactures guidelines. In the event of a mishap we have the option of the morning after pill and termination.
Circumstances can change beyond one's control and individuals/families should be supported but I don't think its right that anyone can bring children into the world when the odds are so stacked against the child even getting off the starting block eg:
https://www.telegraph.co.uk/news/2018/12/07/mother-ex-partner-jailed-brutal-murder-three-week-baby-judge/Listen to Samuel Davies convicted of murdering the 3 week old baby (above) on this YouTube vid:
https://www.youtube.com/watch?v=0miaNRgJXaoHow were the perps brought up? And had little Stanley survived into adulthood how would he have fared? Sadly we will never know but the odds would be stacked against him raised by such individuals.
All of this puts a huge burden on public services: police, social workers, schools/teachers, NHS, judiciary.
Imo it would be far better if would be parents had to meet some sort of basic criteria.