Tom,
Unfortunately, virtually *anything* we do can have negative consequences. Slowing down the lines of people entering a government building would result in some government employees spending less time working, wasting money already wrung from the taxpayers. It could also give government an excuse to tighten security and violate the peoples' rights further (e.g. no lapel pins allowed inside this building).
Think of the taxpayer money that may have been wasted by British officials in Massachusetts investigating the Boston Tea Party and cleaning up the resulting mess in Boston harbor. Not to mention it gave the British crown a compelling excuse to tighten security and further violate peoples' rights.
To address Clay's question, I don't personally believe there is anything that would *philosophically* prevent Libertarians from flattening police car tires or bombing empty government buildings. However as the experience in Iraq and other places has shown, setting off bombs often causes unintended casualties. I would not recommend such a risky course of action unless things got a lot worse. If done with proper precautions not to harm innocent people, whether an action makes sense largely comes down to what the reactions of the public and of the authorities will be.
One can make educated guesses about official and popular reactions to a hypothetical action based on how the authorities and the people have reacted to similar events in the past. The question is whether the positive effects of these reactions (rallying and unifying resistance to oppression among the people, making officials realize they have overstepped themselves and inspired too much opposition, etc.) would be likely to outweigh the negative effects (harsher actions by the authorities, loss of public sympathy for the pro-freedom cause, potentially compromised ability of persons involved to continue working for freedom, etc.). If not, then an action is not worth doing.
Yours in liberty,
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