I can't tell if they actually believe we sing about Munich or not. Either way, they definitely think it gives them carte blanche to sing about Hillsborough, so they push that narrative as much as possible. It doesn't matter how many times you ask for evidence of Munich songs, the best they'll be able to produce is a ropey video of 3 blokes outside the ground or that SOS video from 13 years ago. The irony is, our fans have to hear Hillsborough songs every single season from United fans and we still don't sing about Munich back.
They're also now using the excuse of the Queen or IRA songs, even though they've been singing about Hillsborough for decades. They'll scrape around for any justification - if they couldn't pretend that we sing about Munich, they'd say we deserve it because we sing 'fuck off Chelsea FC' or some nonsense.
The truth is, if you're having to invent justifications for your behaviour, it's because you're doing something wrong but your brain is trying to trick you into thinking you're the good guy in the situation. It's why they also use dehumanising language when talking about Scousers, as long as your brain can compartmentalise certain human beings as 'not quite human in the same way that you are', then it can justify all sorts of heinous behaviour towards them.
There's a lot in what you say there. Dehumanisation is a tactic used throughout the ages. It's used in all sorts of conflicts. It's difficult to hate people you see the humanity in. It's hard to despise those you can understand and have empathy with.
It's far easier to do so once you dehumanise people and groups of people though. Then, you have little or no empathy for them and you can then give yourself permission to treat them horrendously.
With a lot of opposition fans the facts don't matter. Any narrative that feeds their confirmation bias is gleefully embraced, whilst anything that contradicts it is rejected. They
want it to be true that we sing about Munich in our thousands, and three clowns singing it in some random pub means we all do it. One utter arse throwing a bottle at a coach means we're all scumbags. Five clowns singing IRA shite towards Union flag wavers means we are all terrorist sympathisers. They want this to be true. They need it to be true. Because it gives them permission to see us all as less than them. It gives their vile hatred permission to show itself. It means they don't have to care or have empathy because they don't see as human enough to warrant it.
Right-wingers use dehumanisation all the time. They do it with immigrants and benefit claimants. They do it to create scapegoats and divert critical attention away from themselves. It was done to this city by Thatcher and her media cohorts. It was done to us all after Hillsborough. Disgustingly, we've been portrayed as less than human for so long now by our own country and its media. It's no wonder so many people now feel they have the right to pile on and mock the deaths of our loved ones. To them, we don't count. In their self-righteous ivory towers they look down from, we are not worthy of their empathy.
So, do they genuinely believe we sing about Munich? No, I don't think they do. But they want it to be true, so they peddle the lie anyway. Truth doesn't actually matter in the dehumanisation game. All you have to do is say it and keep saying it. So long as it's true in their minds, it gives them permission to absolve themselves of their dignity, their empathy, their morals and their human decency. It allows them to hate whilst still feeling superior.