A rooftop protest by two men dressed as Batman and Robin shows the depth of feeling felt by parents denied access to their children, says Oliver Letwin.
Parents and grandparents demonstrate outside Downing Street
But the Conservative home affairs spokesman stopped short of endorsing the demonstrators, who plan to stay on the roof of the Royal Courts of Justice in London for a week.
Fathers for Justice campaigners Jolly Stanesby, from Ivybridge, Devon, and Eddie Goreckwi, from Romford, Essex, want to highlight the treatment of fathers in the family courts.
Mr Letwin told BBC News Online: "I think more is to be achieved by rational argument and petition than by a stunt.
"Nevertheless what the stunt does is to demonstrate that this is .... this is something that a very large number of our fellow citizens have a first hand experience of and feel passionately about.
"And where passion and reason meet, there's good reason for legislation."
Mr Letwin joined parents and grandparents handing in a petition at Downing Street and he then addressed them in a committee room at the House of Commons.
He said there should be a "presumption" of access for both parents - except when this was deemed to put the child at risk.
"Much as policing matters, much as recapturing the streets for the honest citizen matters ... we will never make a real impact on crime and disorder in Britain until we recognise that not all but almost all of children who get on that conveyor belt start with some serious deficiency at home."
He added that 40% of adults in jail were previously children in care.
"We could make a significant impact on the number of children who do fall on the conveyor belt to crime if we could increase the number of children who are nurtured by their parents."
It did not require training in psychology to work out that it was "jolly nifty" for a child to have some parents to relate to.
Mr Letwin gave campaigners his support
Nearly 40 MPs from all parties have signed a House of Commons motion that argues there should be a "legal presumption" of contact so both parents, in cases where they do not live together, could "continue to parent their children".
The motion also stresses the benefits for children of contact with "any grandparents and extended family members able and willing to play a role in their upbringing".
Anne Harris, the national campaign co-ordinator for the Equal Parenting Coalition and the chairman of the St Neots abuse project (SNAP), said that just because people divorced or separated did not mean they were an unfit parent.
"There are bad fathers, we know, but there are also bad mothers and in many relationships taking place now more children are being abused than they would be by their natural parents," she said.
Pamela Wilson, of the Grandparents Action Group in Shropshire, said that past issues over access had meant she had gone without contact to her own grandchild for two years.
That issue was now resolved but her experience had persuaded her to remain involved in her campaign group.
Joy, 61, from Surrey said her son had a 12-year relationship - including six years of marriage - to his partner who ended their relationship with a note scribbled on the back of an Inland Revenue envelope.
She joined the lobby of Parliament partly in her own right as a grandmother but also on behalf of her son whom she says only has very brief access to his daughters.
"My son's wife wanted him to go, she told him the marriage was over, and she went off with her best friend's husband.
"She wanted ... out of the house so that the boyfriend could move in.
Alison from London said that she had been battling for equal access to her children since her ex-husband moved out with her children alleging she had physically abused them.
"I understand why the courts have to take these allegations seriously but he used them as a weapon against me.
"I've lost a year of contact with my eldest son, I still see my five-year old, but I feel the legal system has let me down.
"It's not just fathers in this situation but mothers as well.
"The fight for my my children has cost them their inheritance - it's cost me £50,000.
"Last week I got a shared residency order but I still have no contact with my eldest son because my ex-husband has turned him against me."
Ian from Cambridge said he had come to London to highlight the "injustices" in the family court system.
"My situation is that I am the father of an eight year old child. I separated from the mother when he was about 10 months.
"She had complete control of contact and for the first few years that wasn't an issue ... and then when she suddenly decided to cut back on contact and refused to negotiate I went to court thinking I would get back the contact I used to have.
"The courts weren't interested in what happened prior, they said they were only interested in going forward from here.
"They're not interested in whose the better parent, not interested in whose got the time, money, love, motivation, enthusiasm, not interested what the child wants to do, only interested in what the mother wants to do."