Did the club break the law in it's promotion of an ideal---No
Have the players did anything illegal---No
Do the players have the right not to participate in a promotion due to Religious Beliefs---probably with a high degree of certainty yes, also based on the clubs actions and acceptance of the players not doing so.
Would the club promote a religious group in the same manner considering that too would be an ideals based promotion----probably not and i would agree with this stance also.
Would players boycott a game promoting a religious group on the jersey---high degree of certainty yes and i would agree with this stance also.
So the players basically did nothing wrong and were probably well within their legal rights to boycott the game, the club did nothing wrong legally in promoting an ideal, the club didn't "force" the players to promote the ideal or threaten to sack based on their views or actions so where is the problem other than the stupidity of a club going down the path of preaching and pushing ideals.
You can't make people have the same views, it's not illegal to have different views, where is the "acceptance" of different views in this case---it's all think like us, promote like us, you are wrong and outdated if you don't think like us.
Not once have the players threatened anyone with opposing views to them or did anything illegal towards the LGBTQ+ community, so where is the problem here.
If the club is not happy with the players stance, pay them out(probably legal ramifications if they did so) or don't resign said players when their contract is up----good luck with that mentality and effectively pushing away a huge number of players wishing to sign with the club if Manly continues to go down this non neutral path of promotion.
The club can still promote "inclusivity" or "LGBTQ+" in a manner that shows the clubs stance without bringing the players into the equation. For example a company can promote RUOK day or Cancer awareness yet the employees don't have to promote it or wear uniforms promoting the day while still going about their work duties that they are paid to do.
Turning up to the workplace has nothing to do with your ideals or views or sexuality, you are paid to perform a role and that is it. The players are paid to perform as a Rugby League player and promote the brand for awareness reasons in the market place not it's ideals.