Williams had a dispensation not to wear the logo under the conscientious objection clause which has been in the NZR contracts for about a decade.
Listen: Neil Sorensen on the Radio Sport Breakfast
"He's a young man it probably won't be the last mistake the young man makes. I'm 55 and still making mistakes - so long as you learn," Sorensen said.
Sorensen said the union welcomed the challenges of operating in a more diverse society, and said ignorance needed to be overcome.
"There's so much ignorance - it is classic human nature when you don't understand things like religion etc you tend to be negative," he said.
"I understand the vitriol on Facebook, I understand it is part of life. Thirty years ago homosexuality for me was "yuck ... you gay w!@#$%"
"I've learnt over the years to be a lot more open and tolerant."
Sorensen said he was "really proud" of the way sponsors BNZ, AIG, Investec and ASB "have accomodated this".
"It's business as usual for them..they would prefer to have everyone wearing their logos but all of them totally respect his decision.
"Don't forget in their industry those corporates cater for all shapes and sizes."
And Sorensen said Williams was an outstanding character.
"He doesn't abuse alcohol, doesn't do drugs, doesn't beat women, he's just a good bloke," said Sorensen.
"If we had more Sonny Bills in the world, we might have challenges around belief systems in our society but we would be better off with 100 more Sonnys."