"That was an act of rebellion"
Colonial tea smugglers paid the Tea Partiers to dress up as Indians and dump the tea because the King gave East India Company exclusive tea importing rights AND cut the tea tax, which made smuggling less profitable.
"Resisting the Tea Act
This 1775 British cartoon, "A Society of Patriotic Ladies at Edenton in North Carolina", satirizes the Edenton Tea Party, a group of women who organized a boycott of English tea.
In September and October 1773, seven ships carrying East India Company tea were sent to the colonies: four were bound for Boston, and one each for New York, Philadelphia, and Charleston.[35] In the ships were more than 2,000 chests containing nearly 600,000 pounds of tea.[36] Americans learned the details of the Tea Act while the ships were en route, and opposition began to mount.[37] Whigs, sometimes calling themselves Sons of Liberty, began a campaign to raise awareness and to convince or compel the consignees to resign, in the same way that stamp distributors had been forced to resign in the 1765 Stamp Act crisis.[38]
The protest movement that culminated with the Boston Tea Party was not a dispute about high taxes. The price of legally imported tea was actually reduced by the Tea Act of 1773. Protestors were instead concerned with a variety of other issues. The familiar "no taxation without representation" argument, along with the question of the extent of Parliament's authority in the colonies, remained prominent.[39] Some regarded the purpose of the tax program—to make leading officials independent of colonial influence—as a dangerous infringement of colonial rights.[40] This was especially true in Massachusetts, the only colony where the Townshend program had been fully implemented.[41]
Colonial merchants, some of them smugglers, played a significant role in the protests. Because the Tea Act made legally imported tea cheaper, it threatened to put smugglers of Dutch tea out of business.[42] Legitimate tea importers who had not been named as consignees by the East India Company were also threatened with financial ruin by the Tea Act.[43] Another major concern for merchants was that the Tea Act gave the East India Company a monopoly on the tea trade, and it was feared that this government-created monopoly might be extended in the future to include other goods.[44]"
http://en.wikipedia.org/wiki/Boston_tea_party
So it was the REDUCTION in tea tax that really pissed off the "American" smugglers.