It's to protect you and your child, carry the birth cert, or a copy of it. Border control have so much to do that you know nothing about, and which you shouldn't have to worry about, if someone else went through with your child I bet you wouldn't be happy then either, u don't realise how common trafficking/kidnapping/taking without permission from mum or dad goes on
Exactly this.
I've said this before in a similar thread, but I can promise you that they do not give a shit if you have fifteen DC, all with different fathers and different surnames. Get married and divorced more times than Elizabeth Taylor. They don't care. They are not making any moral judgments on your relationship or marital history. They aren't picking on you because of your gender or marital status. They don't have quotas. They have a million and one rules, regulations and policies to remember, covering every nationality in the world. Even if they had the inclination to judge you, they don't have the time. Some are polite and friendly, some are dickheads. Exactly the same as anywhere else, be it SAHPs, doctors, teachers, retail, etc. However, all they care about is doing the best they can to make sure that you aren't doing anything nefarious. If you think that someone has been rude to you, then complain. In writing afterwards if you don't feel up to it at the time. But, OP, in the kindest possible way, what you may have considered to be a lecture could well have been an attempt to explain to you what they were doing and why it would be easier for you to carry certain documents in the future. It's easy to feel as if you're being criticised if you feel sensitive about these issues anyway.
It's very easy to complain about having to carry these documents and ask why parent's names don't appear in passports. And if the laws were in place to compel parents to follow an exact procedure, or passports contained that info, then Border Force Officers would probably be over the moon because it would make their jobs much easier. But both of these things are things which Border Force have no control over. They don't make laws and they don't issue passports or get a say in what information goes in them. Lobby your MPs.
UKHTC has many case studies of what happens to children who slip through the net and there are many publicised cases of estranged spouses/partners whisking the children off to some country where their return can't be enforced. Surely it's better to take ten minutes answering questions than risk a child going through one minute of what some of them are forced to endure? Read the case studies on the UKHTC site and try to remember it's about them, not you.