The Democrats didn't even seem to realize they had a problem with Nader dividing workers and environmentalists. A lot of people like to think of themselves as environmentalists, but that doesn't mean they vote that way. Reasonable people can disagree on solutions to complex environmental problems. Unfortunately, too many still think it doesn't matter, or it doesn't matter to them. The vast majority of environmental groups are nonprofit educational groups and cannot do politics the same way that business groups do.
Environmentalist cultures are rife with factions and divisions.
Diversity is valued over unity, and this is healthy, to some degree. But this could be their political undoing in a system requiring unity to achieve power. Increased communications diversity and basic individual empowerment have spawned a plethora of groups divided according to personal preferences. The experience of uniting behind a cause and working productively with people of differing beliefs for the common good seems rare indeed in today's world. These voters feel they justifiably turned their back on the incremental if that progress that the two-party system offers.