Because then the Palestinians will be even more convinced than they already are that if they just keep fighting with Hamas tactics for just a little longer then one more UN resolution will finally come down to abolish the hated Zionist state.
This is not a “pro Palestinian” stance. To believe it is is absolutely fucking deluded. This is an attitude that will lead to Palestinians never accepting a two state solution without a full right of return to Israel proper - which means never accepting a deal that it is possible for Israel to accept.
And that means Israeli moderates working towards peace will be discredited; eventually it could even mean a Prime Minister like Ben Gvir, and then all the things that Hamas’ useful idiots have been squealing about - ethnic cleansing, starvation of Gazans, even genocide - could actually be on the table.
Now, regardless of what the West or the Palestinians do, there will always be plenty of left wing Israelis like myself, who resist that sort of nonsense. But if you make our goal - two independent, prosperous, peaceful states - completely impossible, by legitimizing Palestinian revanchism (“River to the Sea”) and delegitimazing the Zionist project (sEtTlEr CoLoNiAlIsM), then eventually, we will lose to people like Ben Gvir.