i believe you're incorrect. look how long koresh held out against the government. that was just a dozen or so people.
it is dangerous to claim that we can get rid of the second simply because the government has better arms than we do and that we can simply reinstate it if the need arises or if the people are as armed as the government. if you take all the gun owners in the US, i truly believe the government would be hard pressed to defeat them if they united by only a small amount of gun owners.
i also disagree with what you're saying, because it could be analogized to saying - well, the government is more equipped to stifle any speech, monitor any speech, censor any speech, thus, we no longer need the 1st amendment. thank goodness we have it, because the government has in fact tried to stifle speech and lost in court dozens of times in the past few decades. imagine if we had let the first amendment go because it was outdated...do you really think the government would reinstate it simply because, say the internet was invented?
Koresh held out so long because of the children with him, not because he was so well armed. His fate was never in doubt.
Speech did not kill 20 children in Ct last week, but if it did we could have that debate. The purpose of freespeech is still ALIVE and WELL. The justification that guns would allow citizens to attack the government is not.