"I have a daughter" is a reason some men give for their feminism or sympathy with feminism.
It's one reason among many for becoming a feminist ally, but men should be careful of what is sometimes implied with it:
- that all fathers of daughters are feminists: obviously false, but sometimes fathers speak as if feminism naturally follows from having a daughter
- that it's understandable that men without daughters aren't feminists: just because your personal feminist beliefs arose from considering your daughter's life doesn't mean that all men can or should require such an impetus
- that the point of feminism is protecting a girl or woman you care about: feminism extends to the rights of all women regardless of your personal feelings for them, and protecting women isn't the point