I don't think it has to do with equality really, but when we are talking about herediary titles and their historic background, then the difference is to show where the "real" bloodline comes from. When a king marries, it is clear that his blood is the one which will give future rank and precedence to his heir. But if it's a queen regnant, the difference in her and her husband's rank shows that it's her august bloodline that counts, not his.
You can have equality and still identify the bloodline (they are different issues to me).
To keep the bloodline simply stop either gender taking the rank/title of their partner. That makes both genders equal AND still has the bloodline identified.
Charles will be King and his bloodline will pass to William. Why then should either of their wives get a title just for getting married?
Andrew's daughters can't pass on their title and status because they are female and so their children's bloodline won't be able to be as easily identified. (I know why they don't get to pass it on so please don't someone come on here and quote the 1917 Letters Patent)
An exception had to by made in 1948 to allow the present Queen's children to get the HRH. Princess Margaret's children don't get their titles of Lord/Viscount Linley and Lady Sarah Chatto from their mother - the royal - but from their father who was given a title for simply getting married but their position in the line to the throne and thus their bloodline comes from their mother but that isn't reflected in their titles.
The same applies to Anne's children - no titles but closer to the throne than a range of Dukes etc but their bloodline isn't reflected in their titles.
So obviously their is no need to identify the bloodline as there are a number of people with bloodlines closer to the throne than some HRHs who will pass on titles.
Equality would see all the grandchildren treated the same - e.g. all having the HRH or none, until they become the children of the monarch. The spouses of Margaret and Anne would have gained the same status/titles etc as the spouses of Charles, Andrew and Edward. As things currently stand women are second class citizens in passing on the identifiable bloodline as if the bloodline goes through them there is no way of knowing.
The men have titles to pass on but the women don't. Men raise their wives but women can't raise their husbands. That is inequality and it is that that I object to.