It helps because it signals to the DNC that they will not simply automatically win by default with their shittiest, most rightwing nominees because the other option is slightly worse on a couple of fronts.
It shows that people do not see them as a viable alternative to the GOP unless they actually become an alternative to the GOP.
There's a reason why Trump won last time and it's this attitude of entitlement that you've embodied which is at the core of this.
If you're so set upon preventing another Trump presidency then recent history is a lesson for you, or at least it should have been, and attempting to browbeat people into voting for detestable DNC nominees is a failed strategy when you should be pushing the DNC for compromise with people further to the left of you rather than demanding that people further to the left of you capitulate simply because you feel that they ought to because you have a false sense of moral righteousness.
You want my vote for the democratic nominee? Then uphold the values of bourgeois electoralism and earn it.
This is the point where, if I was an organiser in the UK, I would start pushing really hard for raising awareness about how the watermelon is symbolic of support for Palestine and I'd start organising watermelon-based protests, including the strategic deployment of watermelons left at the entrances to Zionist organisations.
If they want to push demonstrations for Palestine underground, so be it. Getting arrested as a prisoner of conscience in the UK isn't going to serve the interests of Palestinians.
But imagine how fragile and absurd the Zionists would look if they tried to suppress the celebration of watermelons and public watermelon eating events or if people started getting brought up on terrorism charges for "accidentally" leaving a shopping bag with a watermelon on the steps of buildings.
Not only would judges be virtually forced to throw out any charges laid against people for this stuff but it would be an absolute media coup to have big Zionist organisations playing victim by cowering in terror at a watermelon left on their steps.