One of the most interesting aspects of Sun Tzu's work on strategy is his perception that fatal flaws come not from the absence of virtue, but by virtues taken to extremes. Sun Tzu's lists five characteristics required for leadership (intelligence, courage, etc.). Limitations in those characteristics may limit your progress, but it is the excesses of those characteristics that can get you into real trouble. For example, the excess of courage is fearlessness, which is literally blind to trouble.
The current problems of the Democratic Party often arise from virtues taken to the extremes. Though the Democrats continually call the Republicans extreme, too often it is the Democrats who take positions that go well beyond the borders of common sense and certainly beyond the borders of good, long-term strategy.
For example, the right to privacy from the government is a good idea. However, this article,
by Rich Lowry gives a good example where the ACLU takes the idea of privacy to the point where it becomes indefensible. The ACLU sought to block the results of government AIDS testing of babies from being revealed to the baby's parents. This prevented the treatment of infections from AID, condemning many of these children to death. The political machinations for this aside, these extreme, non-sensical positions undermine legitimate privacy positions, making them more difficult to support.
Another important movement, the environmental movement, is making the same mistake. One of the biggest human tragedies of the twentieth century was the thirty million needless deaths, mostly of children, from malaria. These deaths could have been prevented by intelligently limiting the worldwide ban on DDT. This tragedy continues today. More millions of lives could be saved by simple clean water programs that have been proven to be so effective and were once the focus of the movement. However, environmentalist spend nearly no resources or efforts in that area anymore, choosing to focus on causes that are much more extreme.
It seems that reasonable, common-sense progressive positions that everyone can support have lost their appeal for influential elements in the Democratic Party. Only extreme positions of questionable value are currently appealing. The question is why? Sun Tzu teaches that the answer comes down to character. An extreme sense of ethics forces some to take positions that a well beyond the mainstream sensibiltiies.