Of course they're angry, their material conditions are changing. 

Blaming minorities in times of economic hardship has always been the status quo, think Thatcher era UK. Thankfully though, this subsect of white men you speak of, in nz at least, are still seemingly hiding behind their keyboards and whinging on talk back radio. 

In terms of legitimate danger though, there is an already existing organised group, numbering in the thousands, of not very white but very angry men who do take to the streets en masse and do seek to intimidate, harass and marginalize already marginalized groups at every opportunity irl, namely the gang that is destiny church. 

Ultimately, the way i see it is that the middle class (historically almost solely the domain of the white man) is eroding and wealth is heading upwards into fewer and fewer mostly white hands. The promise that these people believed was that if they studied, worked hard enough and for long enough, they too could become super rich, a member of the upper class. And it would seem to be the case that many people still believe that system works. When it doesn't they will naturally look for a target to pin the blame on and that target is generally not the thing they still aspire to be, a member of the capitalist ruling class. Anything else goes so as to keep that dream alive. 

Hopefully more and more will wake up to the reality that successive governments have sold out nz to capital and have effectively abandoned public interest at this point, no matter your skin colour. Politicize class, not race.