You're conflating some quite different things here. Most uses of cluster munitions are war crimes, yes, because most of the time they're used in exactly the same way Russia is using them - by an invading army who is at best eking out a military advantage and heedless of the long-term damage done to the civilian population, and at worst as part of active terror tactics to try and kill civilians and force a surrender. That's a war crime, no two ways about it, and the fact that they're so widely used that way is an excellent reason to have treaties in place banning their use. But this is a very different statement to use of cluster munitions being against international law or a war crime in and of itself. They're not chemical weapons or nukes. The problem with them isn't that they're inherently worse or more evil or inhumane than any other weapon in their effect on enemy troops, but that it's very easy to use them in evil ways against civilians and that the damage they do extends long past the end of the war. In this very specific situation it would be insane for Ukraine to use them in evil ways, most of the long-term damage has already been done, and that small part of it that hasn't should be Ukraine's own decision.

You yourself admitted in another post that it's very unusual for cluster munitions to be used by a defending army. Given that, I don't think "most uses of cluster munitions are war crimes" is a good argument, and it's still coming down to this idea that we should stop the Ukraine government from having cluster munitions in order to protect Ukrainian civilians. The same Ukrainian civilians who are now half-soldiers themselves by necessity and who desperately want those cluster munitions to stop the Russians from killing them, throwing them into re-education camps, and stealing their children to send to Russian "orphanages" whether their parents are alive or not. Do you understand why I think that's so fucked?

If Ukrainian use of cluster munitions would inherently constitute a war crime or violate international law, then I can see a coherent argument for not sending them - as awful as the situation is, further weakening international law has the potential for even worse consequences down the line in future conflicts between other powers. But if that's true, I'd like to see some actual evidence in the form of e.g. a statement from a respected bipartisan legal organisation saying so. So far I haven't seen anything of the kind in the media, or even from bipartisan organisations calling for America not to provide them - for example, while Amnesty International is against the US supplying cluster munitions, they certainly don't say it would violate international law or be a war crime. The argument I've seen from organisations like this is that using cluster munitions here is a retrograde step away from one day making these treaties global and banning cluster munitions worldwide - this is true as far as it goes, but nowhere near enough for me to ignore the clear and present harm that using them here would help to avoid.

If instead there's no war crimes or violation of international law, then to convince me sending the munitions is wrong you'd need to prove that giving Ukraine the weapons they're asking for to defend themselves is going to do significantly more harm to them than a Russian victory, and that's a very high bar to clear.