Thoreau's attitude towards government is best expressed in his essay "Civil Disobedience." This essay starts with a phrase that is commonly heard today: "That government is best which governs least."
As a Transcendentalist, Thoreau believed that people should follow their own consciences rather than doing what society expects of them. This idea can very often be at odds with the idea of having a government. In Thoreau's case, the government believed that fighting Mexico in the Mexican-American War was the thing to do. Thoreau believed it was wrong and therefore refused to pay his taxes.
So -- Thoreau believes that government is bad because it tends to prevent people from following their consciences as they should. This led him to say "That government is best which governs not at all" soon after the line I quoted above.
Thoreau declared in his "Resistance to Civil Government," [later titled "Civil Disobedience"],"that government governs best that governs least." Clearly, Thoreau understood the dangers of a "Big Brother" government that does not allow people to think for themselves, and the importance of individual responsibility. He, like other Transcendentalists, privileged the innate wisdom of the individual over church doctrine and law. The thinking individual who feels responsibility to mankind does not violate laws, and, as such, he does not need an oppressive government that dictates to him what behaviors he can and cannot have.
In today's American society, Thoreau would be appalled that people do not possess individual ethics and only arrest their aggressive business or unethical behavior if they run the risk of violating a law. He would also be appalled that individuals do not think for themselves, relying on the government to provide for them, as well as making sweeping dictations upon their personal behavior. (e.g.wearing of seat belts, talking on cell phones, smoking, uttering certain words in public, etc.) Indeed, Thoreau would be disappointed in people's personal conduct, unthinking actions, and passive acceptance of the dictates of the government. He would be chagrined that Americans have not transcended their "lower selves and their society."