Addendum: A better way to define it would also have been to say that the spell effects themselves aren’t directly what leads to such harsh punishment. Instead, they carry symbolic meaning, and are the signature spells of the Death Eaters, that were appropriated by them.

So basically, there are alternative spells you could use to achieve similar effects – but by using one of these 3 particular ones, you are outing yourself as a Wizard Nazi. So basically the spell form of a swastika, wolfsangel, sonnenrad, etc.