The desire for power is not a vice that afflicts only "bad guys". Often "good guys" will attempt to acquire power in order to force their ideals on others (ostensibly for their own good) or else to keep power out of the hands of the "bad guys". Unfortunately, however, history bears out that "good guys" who seek power for these purposes often become the worst of the "bad guys" because they pursue their goals with the approval of their conscience.
"Good guys" that seek power for such aims are suspicious of anyone who stands in their way, viewing such people as either misled or else one of the "bad guys", but, either way, a threat to what is "good". They resent even being questioned. This is how dissenters become 'enemies of the State', and ultimately victims of its oppression, even when "good guys" are in charge. This is also why legislation such as the Patriot Act, the Military Commissions Act (among others) and the concepts that "unlawful enemy combatants" and "terror suspects" have, essentially, no rights at all, and that torture is really a good and necessary thing, are going to end up destroying the freedoms and enslaving the people they were ostensibly meant to protect.
The only thing that can protect freedom in the long run is a staunchly upheld separation of powers, emphasizing individuals rather than artificial entities such as the State (and unquestioning loyalty thereto).
One sure-fire way to tell when you're heading downhill fast under a tyranny of "good guys" is when they bristle at being questioned and demand the right to operate in secret. When this happens - as it is now happening - look out.