It is certainly possible to argue that the colonists were not justified in rebelling against Britain. Although the colonists portrayed the British government as a tyrannical despotism, it is easy to dispute this portrayal.
The colonists had two main reasons for rebelling. First, they felt that the British government was taxing and regulating them excessively. We can argue that neither of these is true. The British government did place taxes on the Americans after the French and Indian War. However, the taxes were not as high as the taxes that British subjects in England paid. In addition, we can argue that it is not unreasonable for a country to require its colonies to pay some of the costs of a war that benefitted those colonies. This may be grounds for political protest, but surely not for a war.
Second, the colonists felt that they deserved to be represented in the British Parliament. This seems like a legitimate desire, but we can argue that it was not enough to justify a war. First of all, the colonists did get to have some degree of self-government within their colonies. Second, not everyone in England was represented in Parliament either, so the colonists were not being treated worse than all Englishpeople. Finally, we can argue that it is excessive to start a war simply because you want more political power.
Finally, we can argue that the colonists brought some of their troubles on themselves. Their protests against British taxes and regulation were, we can argue, excessive. The Boston Tea Party, for instance, constituted the destruction of large amounts of valuable property. If political rebels burned down a government building or otherwise destroyed property in the US today, we would expect that they should be punished. We would not think that the punishment was abuse.
In short, we can argue that the colonies were rebelling against a legitimate government that did not abuse them excessively. We can argue that the colonists exaggerated the degree to which the British were tyrannizing them and that British actions were not severe enough to warrant a rebellion.