There are several points to consider when answering this question. I will explain some of the main ideas so you can draw your own conclusion.
The first point to consider is whether destruction of property is acceptable. The dumping of the tea into Boston Harbor was a very expensive act. This action cost the company a lot of money. Was there another way for the colonists to get their point across without destroying property? Is there ever a time or circumstance when it is acceptable to destroy property?
A second point to consider is were the actions of the colonists appropriate for what was making them angry. The colonists were upset because of tax on tea as well as the monopoly that the British East India Company had on the tea trade. Were these concerns significant enough to respond in the way the colonists responded?
Finally, were the colonists willing to accept the consequences for their actions? Whenever a group of people protests by breaking the law, the group must be prepared for the consequences that will follow. The colonists seemed very surprised by the British response to their actions, which was the passage of the Intolerable Acts.
In considering these points, you should be able to decide if the colonists were justified in their actions at the Boston Tea Party.