Folau has found few supporters in the rugby community after attacking gay and transgender people on social media last week, which led to Rugby Australia terminating his $4 million contract, pending an upcoming hearing.
Folau confirmed to RA on Wednesday that he wanted a hearing to fight his dismissal, rather than accepting his fate; though his place in Australian rugby appears untenable whatever the outcome.
Genia followed Wallabies coach Michael Cheika in saying that he did not expect Folau to play for Australia again.
"I firmly believe what he did was wrong and how he messaged it, put it out there was wrong," Genia told the FOX Rugby podcast.
"You can't be out there spreading hate and telling people that they're going to go to hell.
"You can have your beliefs and have faith in what you want to have faith in, but you can't go around trying to tell people they should be going to hell because they are a certain way. For me, that's completely wrong."
Folau is expected to argue that his contract did not specify that he couldn't air his strong religious views on social media.
It has been reported that Rugby Australia did not make specific provisions for Folau when it re-signed him in February for $1 million per season, despite a similar earlier homophobic outburst.
RA chief executive Raelene Castle has said Folau was repeatedly warned that he could not vilify LGBTIQ+ people on social media; though doubt has been cast over her own future in rugby, should Folau be found not to have breached his contract.
Genia said that whether his contract prohibited such behaviour or not, Folau had betrayed the trust of Castle and Cheika.
"If you've gone and said those things to Cheika and Raelene, there's a breach of trust and I guess there's an element of selfishness about it as well," Genia said.
"You can have your beliefs but at the end of the day, you're also contracted to Rugby Australia and the NSW Waratahs, who as your employers stand for certain things in society, who want to promote the game a certain way.
"Obviously being inclusive of gender, sexual preference, religion, background, whatever it might be.
"So when you sign up to your contract to do that, you adhere to those rules, you adhere to what's been set out before you by those two organisations and I think the fact that he's gone and said that he wouldn't do such things and say any more about what he did last year, he's obviously broken a bit of trust with Raelene and Cheik.
"I know that Cheik is someone who respects him massively. He's got a lot of time, a lot of love for him and has supported him all the way through.
"I know that he'll be very, very disappointed with everything that's happened, for sure. I don't think I'll get the opportunity to play with him again, definitely."
Genia, a 100-test veteran, stressed Folau had not merely offended the wider rugby community, but his teammates with his extreme views.
"Izzy can have every right to believe in the things that he wants to and have faith in the things he wants to have faith in, but he's got to realise that there are other people within that group, both at the Waratahs and Wallabies, that have certain beliefs as well, that very much conflict with what he's come out and said and done," Genia said.
Despite his condemnation, Genia said that he knew Folau as a "lovely, humble guy" - making his homophobia even harder to process.
"So for him to come out and have said and done the things that he's done, it makes it pretty uncomfortable for a lot of people," Genia said.
It looks increasingly unlikely that Folau will ever play for the Wallabies or Waratahs again, though success in his appeal could enable him to be paid-out his $4 million contract.