It doesn't stop you including him in the decision making process. You just want to make that all legal and official.
The law says that he con't do that with your children unless he does that with you first. If you don't view the legal commitment of marriage as important, why do you see the commitment of parental responsibility as something important?
I haven't assumed one way or the other whether it's you or him who doesn't want to get married - just that it must be at least one of you. And it is my personal opinion. Don't mind if you disagree, but you'll have to campaign for a change in the law.
You could always apply for a shared residence order - perhaps one involving the natural father as well assuming he exercises overnight contact. That way your partner would acquire parental responsibility.
However if he were to acquire PR and you're not married, he would preserve PR (unless the court removes it from him) even if you separate, and you would have no claims against him in relation to your children for either maintenance or capital provision, yet he would still be able to, for example, prevent them from going abroad, and obtain medical information and education records. If you are married, he may still have some financial responsibility towards your children.
PR isn't about money per se, but part of responsibility includes the duty to house and provide for. The court/state can only enforce that if you've been married, so presumably the legislature didn't want to allow those who weren't prepared to make the direct commitment of marriage (and therefore the indirect commitment of financial responsibility towards the children) to assume all other responsibilities towards the child. The thing is, as I'm sure you'll agree, to be a parent you'd put your child's financial needs above your own. If you have no financial responsibility to start of with.....