I do think it's one of those particular decisions though that it's very common to be a firm 'no' on in your 20's before it being a yes in your 30's, so I do think the likelihood of a change of mind should be part of the whole picture.
Anyway,I'm not saying you shouldn't be able to choose, far from it, but more that if you do, it's your risk that you undertake in the full understanding of the concequences.
It's also very different from people regretting having children. There are many children who, after having children, regret not staying child free, but they also love the children they had and don't regret having them specifically, if that makes sense. Even those that regret children are generally horrified by the idea that they could give up their children for adoption, or hypothetically click their fingers and they didn't exist. My understanding is that it's a much more complex regret and mixture of feelings than this.
There aren't many decisions in life which will irriversibly and delibrately shut off avenues in life. You could marry and move to a different country, for example, and you'd be giving up the UK and family here, but you could move back if unhappy. Jobs and career paths can be changed.
So I can understand that the decision to irriversibly shut off having children (reversal isn't easy for women) needs to be taken seriously, and I think if given on the NHS, it should involve compulsory counseling, and a cooling off period. But ultimately, as an adult, it's your risk to run and your wish should be respected.
I do think that given you have a partner, him getting a vasectomy might be better, as it's easier, and in the event that you both did change your mind, then more realistic to reverse. As unlikely as that seems now, a plan b is just your looking out for all the possibilities of the future.