Views are one thing. But if a workplace has a policy in place, and that policy is in line with the law, an employer has every right to ask the employee to follow it. He has no right to decide on who to employ based on his own beliefs. He should do what his manager tells him to do.
IF what his manager told him to do was unlawful - that's a different matter.
Aside from all that, if the manager didn't do a very good job in properly performance managing him out since he refused to follow company policy, then he may well win. Reading between the lines, it looks to me like he raised a grievance about his treatment, and in order to investigate they dug up I formation about his activities on the network. They discovered he had been doing other work on company rime using company equipment - a clear sacking offense.
The sticky part will be - if the investigation into his use of the company network was prompted by his grievance, did the employer find and use that evidence appropriately (I.e. was it in the genuine attempt to investigate his grievance against his boss, which then showed up email records etc of him doing his other job - or were they poking through all his records to try to find whatever they could in order to get rid of him in bad faith).
Either way... they have a right to sack him based on what they found, since policy will state they can look into his use of the network at any time. So his case may rest on whether a fair process was followed during the grievance, or whether it was a pile-on that was mismanaged internally because of this woman's personal problem with the guy and his 'belief' that he doesn't need to follow company policy because it discriminated against men.
Not convinced. The implications to employment policy and law would be profound.