Nazism is a genocidal ideology; it's fundamentally evil.
The individual reasons for a specific person to ascribe to such an ideology are complex and worthy of study, and if the quoted statement had been 'any individual member of a fascist ideology is fundamentally evil', then sure - let's pull in the nuance.
But that's not the case here - we aren't talking about individuals, or general social movements, or something else that requires such consideration. We're talking about a very specific ideology.
Nazism - the ideology itself - is not a redeemable thing; it's an ideology inextricably tied to a laundry list of horrific acts.
It's absolutely fine to declare it evil.
Be careful with such statements.
Describing something/someone as "fundamentally" evil obscures the fact that things (like extremist politics) happen for reasons. It is these reasons that if addressed, can put a stop to such unpleasantness occurring.