The main supposed justification for destruction of property would be that it helped the colonies. You could also argue that it was just inherently justified to do anything that taught Britain a lesson, but I'll stick to consequentialist ethics here, since the goal of a protest is typically to help whatever people the protestors are protesting for. The immediate effects of the Boston Tea Party were the Intolerable Acts: closing Boston Harbor, replacing Massachusetts' government, and the Quartering Act, among other things. All these immediate effects were bad for the colonies.
However, those policies also led to the Revolutionary War. So was the protest was justified because it led indirectly to American independence? This gets into a political theory called "accelerationism" which basically argues that we should try to make things get bad faster so that people will protest and overthrow the oppressive system. But I have several issues with this approach. First, it would imply that the Intolerable Acts themselves were justified because they led to revolution. Basically, anyone involved in passing the acts and violating the colonists' rights was actually doing a good thing, because it led to the American Revolution. And at best, you will get lucky with this strategy, because it's easy to predict "this will lead to punitive measures" but hard to predict "this will lead to American independence." The colonies could have easily lost the war, and most colonists didn't even want to fight it until the Intolerable Acts were passed.
So at best, the Boston Tea Party was a way of twisting the colonists' arms into fighting a war for independence (which would end up involving child soldiers), when most of the colonists had wanted to avoid war altogether. A good chunk of the colonists fighting for reforms condemned the Tea Party anyway, with Benjamin Franklin offering to pay for the tea that was destroyed. Many of the grievances with the British government might have been solved without war, and the Intolerable Acts themselves were certainly avoidable.
Now you could say that the people behind the Tea Party weren't responsible for what Britain did, but the goal of a protest is to send a message and influence behavior, so I think protestors (particularly those destroying property) have at least some responsibility not to cause needless destruction.
The most cogent defense imo is that the tea belonged to the EIC, which was granted a monopoly by the Crown, so destroying the tea was a protest against extractive economic practices by destroying the property of a corrupt monopoly. A good moral parallel would be attempts by the Chinese to destroy the Sassoon Opium empire, which also had the military protection of Britain and was openly extractive and exploitative, leveraging their druglord money to invest heavily in Shanghai real estate.
destroying the tea was a protest against extractive economic practices by destroying the property of a corrupt monopoly
Sure, but the effects of the protests were bad for the colonists, and I don't see what positive effects they could have been anticipating. So it was still needless destruction of property.
attempts by the Chinese to destroy the Sassoon Opium empire, which also had the military protection of Britain and was openly extractive and exploitative
A lot of morally questionable decisions were made by China there, like preventing the sale of food to the British, leading to the Opium Wars (which were bad for China). So I accept it as a parallel but it largely proves my point.
