> I am yet to see a clear articulation of 1. What those critical interests are
The critical interest of the US is in avoiding direct war of the US with Russia when it invades Poland or Estonia. Russia _will_ invade a NATO country if it conquers Ukraine, and the US will be obliged to defend it. So if the voluntary support of Ukraine allows to avoid that scenario today, it obviously is critically interesting.
> Why they are worth pursuing at the risk of a/ destruction of European economies b/ alienating China,
Because it is much better to risk the destruction of European economy (btw, how exactly?) or alienate China than risk sleepwalking into a potentially civilization-ending NATO-Russia war.
The critical interest of the US is in avoiding direct war of the US with Russia when it invades Poland or Estonia. Russia _will_ invade a NATO country if it conquers Ukraine, and the US will be obliged to defend it. So if the voluntary support of Ukraine allows to avoid that scenario today, it obviously is critically interesting.
> Why they are worth pursuing at the risk of a/ destruction of European economies b/ alienating China,
Because it is much better to risk the destruction of European economy (btw, how exactly?) or alienate China than risk sleepwalking into a potentially civilization-ending NATO-Russia war.