Masculinity is the nature of being a man so a man hearing the phrase is like being told your nature just for being a man is toxic. Those who use the phrase say no you don't understand, is only a certain kind of behaviour that we're talking about. It harms men too so men should want to get rid off it too. The thing that you're actually talking about then is gender expectations so just call it that. When you say toxic masculinity it feels to men like they are being called toxic for just being men and I think it must be intentional because it would be so easy to use a phrase which doesn't get misconstrued like that. I understand once you listen to the convoluted explanation of what the phrase actually means that it just means "harmful gender expectations/roles" but why use a name which seems almost designed to immediately make men feel defensive and polarise them from any discussion?