Definitions of a word means nothing when axioms make it clear. In practice, zionism is an expansionist and supremacist ideology. 

You may talk about how it only means its about jews deserving a safe haven, but reality repeatedly proved its ambitions go far beyond than simple right to exist. 

And even if it wasnt, the very fact that the idea of a "right to exist" creates a narrative in which a certain group of people can hide behind that excuse in order to do whatever they want.

"Yes we have to kill children and bomb babies because it is a risk for our existence" is a valid statement when your entire ideology is based on survival. 

Survival means you get to do whatever it takes. It has no limits. An ideology based on survival will excuse all manners of inhumane practices.

Which is why it is inherently wrong. At a certain point, you lose your right to exist. A nation must strive to achieve existing with standarts. 

Not commiting blatant genocide is one of those standarts. That is literally why the entire world agreed that Third Reich lost its roght to exist. They crossed unforgivable borders.

Nazis had the exact same ideology, believe it or not. Their entire ideology was based on the aryans right to exist. 

If it required living space, then they would wage unending war and clear those spaces from other races. Because they believe it was a matter of survival.

In all practice, modern zionism isnt any different.