That's like saying German citizens during WW2 should be killed, raped and tortured. Black and white is usually the wrong way to go about thinking.
Without commenting on whether I agree with the screenshot, I'd like to ask a question - what do you (as in, the people who would like to see "Zionism" defeated) think will happen if "Zionism" will be defeated?
You're missing some context - “not voting [instead of] for Harris is a vote for Trump”. If the dilemma is between not voting and voting Harris, choosing not to vote subtracts a vote from Harris.
Of course Harris got a boost in donations after she became the candidate - she appealed the the people who thought Biden was too conservative. That doesn't mean conservative democrats are an insignificant demographic, they simply already donated earlier. The move towards the center is meant to not drive them away into not voting [instead of voting for Harris]. Obviously there will be some progressives and some conservatives who will decide to not vote [instead of voting for Harris], the goal is to move to the point where these margins from both sides will be minimal.