Democrats aren't attacking Jill Stein because they think she is taking votes from Kamala Harris. No one I know who's voting Green would consider a vote for Harris at this point. They're attacking Jill Stein because they don't want voters to know that there can be a worker-centered party to the left of the Democrats that supports popular policies like Medicare for All, a $25 wage and federally guaranteed housing.
There are 80+ million eligible voters who don't vote at all because they don't see the point. Democrats are okay with this, in fact, they don't want any candidate to their left to appeal to those voters with popular policies.
The fact that the Green Party exists shows that the Democrats aren't pushing the most progressive policies. Jill Stein's candidacy shows that it's possible to support reproductive justice AND be against funding and arming a genocide. That we can end homelessness if we stopped funding endless wars around the globe.
Democrats don't want anyone to the left of them to exist because it's the only way they can convince Americans that Dem policies are "the best that we can do". To Dems, anything else is just "asking for a pony".
Don't fall for it. Despite Dem's desire to have you think otherwise, things don't have to be this way.
Another world is possible.
Not only did the Democrats not deliver on the Green New Deal they promised, but they expanded the private prisons at the border https://www.aclu.org/news/immigrants-rights/unchecked-growth-private-prison-corporations-and-immigration-detention-three-years-into-the-biden-administration
What does this have to do with anything? Yes, the Democratic Party is flawed. That doesn't change the fact that voting Green will make my political desires slightly less likely, and will make my political fears slightly more likely, compared to voting for a Democrat.
I have an idea, how about everyone votes for whoever they like? Freedom of choice and all that. I personally don't like racists and genociders, so Harris lost my vote and Trump never had it. I was actually willing to give Harris a chance after Biden dropped but she delivered one insult after another, she clearly doesn't want my vote. Would you vote for someone who insults you or those you care about?
Of course anyone can vote for who they like, or not vote at all, no one's saying otherwise. It's Harris's job to earn your vote, and she clearly hasn't. But pushing third parties as the solution to any problem is going to do more harm than good until we get a better election system. It may feel better to vote for a party that more clearly aligns with your positions, but if they have no path to actually acquiring any power to make change, you're doing nothing while feeling like you did something. Changing the policies of a flawed party that actually has power is much harder, and yes, there might be compromise or half-measures, but that's an infinitely more productive path. (More productive than that is doing direct action outside of the electoral system entirely, but both things can be done at the same time.)
It's not "doing nothing" it's demonstrating that their "viable" candidate is not an acceptable candidate. You're demonstrating that the people reject them and that we have the power to prevent their victory, putting pressure on them to earn the votes of the people, necessitating changes to be made and concessions given if they wish to stay in power.
Unless they can convince all of you folks to abandon your blocs and "vote blue no matter who". Then they have free license to do whatever they want, and to let the other side continue being the bogey man that gets you to the polls, because without you your bloc is too weak to affect their victory.
It's a self-fulfilling prophecy; by saying you are too weak to effect change and arguing as much instead of demonstrating in solidarity with other objectors that genocide is a policy that will guarantee defeat for the Democrats now and in the foreseeable future, because the other side is unacceptable (which implies that your side to you, even if genocidal, is acceptable, because of the comforts you believe they are promising over the other side), then you yourself are participating in the thing that is making you too weak to effect change and in the process throwing those people who are subject to the genocide under the bus in service of your own comfort.