One invited other WDL followers to join him in burning a Koran and joked online about how best to kill black people.
Another talks about driving Muslims out of the south Wales valleys.
Examining the evidence in the special programme, Judge Mark Powell QC said: "It's mindless, its racist, the purpose of what they are doing is to inflame racial hatred…I think from what you have shown me it is criminal behaviour and no doubt something that the police would want to look at."
Shadow Welsh Secretary Peter Hain, who has campaigned for years against racist groups, said: "I think every mainstream politician in Wales, wherever they are based, should make it a priority to talk to young people to explain the WDL is in a long line that goes back through the Nazis.
"And I don't say that lightly because, that is the exact political situation in which Hitler was able to come into power because main stream politicians did not deal with the grievances in Germany.
"Now I'm not suggesting the WDL is anything like as powerful as Hitler's Nazi party became, the WDL is a tiny marginalised party, but once you allow these groups to gain credibility that's where you could end up."
Jeff Marsh, who uses a variety of aliases and wears a balaclava to broadcast online to followers, says he has disbanded the WDL because of the racist element.
He has set up another organisation against Muslim extremists called 'The Welsh Casuals'.
He insisted that the group is non-racist.
Another group calling itself the Cymru Defence League has emerged out of the WDL.
The English Defence League now has around 60,000 followers on the social networking site Facebook and thousands have attended protests around Britain.
Saleem Kidwai of the Muslim Council for Wales said most people are opposed to both the defence leagues and Muslim extremists.
"We have extremist groups and they are as ignorant as the Welsh Defence League, or the English Defence League," he stated.
'Significant threat'
"We can condemn them as much as anyone else. They are misguided youngsters being misinformed and used by extremist ideologues who want to use religion for their own political motives.
"That's how we see it. That's why they are banned in all mosques in Wales because people don't like those extremist views and ideals."
The programme also highlights the potential cost, as police forces are called to marshall demonstrations, both by the WDL and the counter-demonstrations they could spark.
It is estimated the bill to the taxpayer could be as much as £500,000.
Det Ch Supt Adrian Tudway, the national co-ordinator for domestic extremism, advises local forces on the threat posed by the various defence leagues.
"I think it's a very significant threat. It's one I know the police service are taking very seriously, together with the Home Office and local authorities," he said.
"Unmasked: Welsh Defence League" is on BBC One Wales at 2030 GMT on Monday 6 December.
BBC News
