YABU. I'm a radical feminist, and I do not want men to own half of any child they donated some sperm for. Why should they? Let's be realistic here, they don't invest anything much, unlike the mother, who risks her life.
Children should be free, and have the right to live with the person who has been their primary carer since day one, or if that person is for some reason found unfit to raise a child, the person who has been their secondary carer.
If a man never was the primary carer for the child he now wants to have rights over, well, tough shit. I'm not on his side. I'm on the child's side, and the child will want to stay with the person they know best.
And I am pretty sure the men who moan and complain about being "disadvantaged in the family court" actually are not stay at home dads. Or did anything over 50% of childcare. Most probably did nothing at all.
Because judging from the way our society worships men who do about 30% of childcare as heroes, it would be very very weird for family courts to not rule in the favour of such heroes.
(And I actually read that men get to be the resident parent in some 90% of cases they actually ask for it. They just don't want it very often. But I don't know where I read it, so .... disregard it if you want, but the way men are worshipped for doing actually less than their fair share cannot be explained away)
So, no, radical feminists aren't allies for silly MRAs who complain about not having enough male privilege yet.
Though I assume you are being ironic (sarcastic? Whatever, I can't tell that apart) and know very well why those men do not join with radical feminists.