I suspect I'm going to get a pasting here, but consider this.
A man and a woman join the same firm at the same time and do an equally good job on the same pay, which is absolutely right and proper.
The same woman, of her own volition, has a child and 12 months maternity leave, then another, then another, totalling three years off in one hit.
During that time the man gets greater pay rises and earns more than the woman.
In a situation like this, then yes, it is fair that the man is being paid more (but then I'd think exactly the same if the man decided to take three years paternity leave and the woman advanced).
On the whole I think men and women should be paid the same for doing the same job, with caveats - such as above.
Oh, in Tennis too - I think it is fair men got paid more because they play more tennis, although I understand Wimbledon stopped this last year.