An issue which I would like to see Mumsnet throw its weight behind is the legalisation of gay marriage and heterosexual civil partnerships.
Recently, the coalition government announced a consultation on marriage equality, however progress is very slow.
If Mumsnet were to campaign about marriage equality, it would help put pressure on the government to speed up the consultation and make it harder for them to backtrack.
A good website for more information on this issue is Equal Love.