I am vegan and some vegans frustrate me as they can sometimes concentrate on their own personal 'purity' and arguing with people nastily and without listening, rather than trying to find a pragmatic and effective approach which actually makes a difference and helps the things we care about.
EVERYONE should be made to feel welcome to care about animals/their health/environment and make positive changes, not be policed or shunned for not being perfect (none of us are).
However, the Nazi comparison I find irritating and highly ironic. I read somewhere that Hitler based the concentration camp plans on slaughterhouses, dunno if that is true but there is definitely a connection in methods and industrialisation of killing there (you don't have to say they are morally the same, but there are undeniable similarities). Animals don't HAVE to be considered equal to us to have value- eg most people would kill their cat before their mum but they still don't think it's ok to kill their cat to have a burger.