Nobody questions the fact that we have been paying into the EU. But what if we get back more in economic activity and tax revenue? Even Brexiteers mostly agree that, financially, we will be worse off, but that is a price worth paying.
Indeed.
But even aside from that, there's also a basic moral issue: We are easily one of the richer countries in the World, and we are also (albeit by a smaller margin) one of the richer countries in the EU. That means that, you believe in making a better, and a fairer, world for all humanity, then clearly we are probably going to be paying in more than many other countries to any international organisation that we join.
If a wealthy individual complained about having to pay more tax than the pauper down the road, and demanded that his tax bill be reduced to no more than the pauper was paying, I imagine that just about everyone would recognise that the wealthy individual was being very selfish, and few would have much sympathy for his demands. Yet that is exactly the logic of those who demand that we should not be paying any significant net amount into the EU.
Of course, there will always be legitimate questions about whether the basis for setting EU contributions and how the money is spent is fair and wise - that's always true for any similar organisation - or indeed any Government. But it does seem to me that there is something fundamentally very nasty and self-centered in this idea that so many people - including many right-wing politicians, much of the tabloid press, and some people on these forums - put out - that we should leave the EU because we otherwise have to contribute money to it.
In the end, the UK is not the centre of the Universe. It is not the only country in the World. We live as part of a Worldwide community - of which the EU is a part - and as one of the richer countries in the World, by any moral standards, we need to accept a corresponding responsibility - including a financial responsibility - to play our part in that community.