The third plank in Sean Faircloth's new atheist strategy is the most straightforward and easiest to explain.
I have already discussed the fact that the key to political effectiveness rests in the number of dollars and the number of votes one can bring to the political table.
Well, if Person 1 comes to the table with V(1) votes and D(1) dollars, and Person 2 comes with V(2) votes and D(2) dollars, then a coalition comes to the table with V(1) +V(2) votes and D(1) +D(2) dollars.
Okay, yes, there may be some overlap in membership and patronage, but, to the degree that there is no overlap, the point stands. And where we are talking about local organizations forming an international coalition, we should see less overlap.
There are a few arguments to support the practice of having a coalition of diverse organizations over a single large organization. One of those reasons is something that any student of biology can understand - diversity. A diverse population is more versatile, better able to survive changes in the environment, and better capable of growing stronger over time (evolving) than a population of one genotype. As different subgroups thrive and fail, the population benefits from the survival of the fittest and evolves.
Somebody who sees evolution as "the enemy" likes to characterize survival of the fittest to mean attacking and destroying everybody else. In all honesty, these are hate-mongering bigots seeking personal advantage by bearing false witness against others - contemptible low-life creatures seduced into hatred.
Really, those people seek to elevate themselves by selling hated and fear. Against "Darwinists", this means selling the message that "survival of the fittest" means that those who consider themselves fit must seek to slaughter everybody else. That Would be a good reason to hate and fear "Darwinists" if it had any foundation in the truth. It does not, of course. However, to the stockholders in groups that can rake in profits by selling hate and fear - which is exactly what many creationist groups are - truth in advertising has never been a high priority.
Surprisingly, they are creatures that use and seek to profit from the very same practices - promoting themselves by unjustly inflicting harms on others - that they condemn as the morality of "Darwinism". However, where hated, fear, and intellectual and social irresponsibility lurk, we should not be surprised to find hypocrisy as well.
The rest of us only have to look to nature - colony animals like ants and bees, herd animals, flocks of birds, schools of fish, and even relationships across species such as that between bees and flowers to see examples in which the fittest seek to cooperate with others. In human societies, we see the advantages of specialization, division of labor, and trade. The "fit" human is not living by himself in the wilderness, hunting or growing his own food and taking care of his own needs for shelter and medical care. He is a member of a community where he can focus on developing a useful skill and trading with those who have other skills.
The same applies to a diverse group of secular and atheist organizations.
To begin with, different people have different tastes, interests, and concerns - even if there are areas where they overlap. There is more than one flavor of soda, more than one restaurant, more than one type of game, more than one type f television show - because people have different tastes and interests. "One size fits all" (or "one group for all secularists and atheists") is a strategically poor choice.
A diverse set of groups promises to bring in more members. A secularist - a proponent of the separation of church and state - would not join an atheist club, but could join a group concerned with church encroachment into politics. A theist who accepts the scientific fact of evolution can join a group opposed to creationism in the classroom. A psychologist or social worker who cares nothing about religion can join a group that focuses on eliminating stereotypical and bigoted messages that contribute to bullying in the classroom.
Local and regional concerns are best addressed by local and regional groups - whose ability to add weight to a national campaign having local implications is invaluable.
The secular and atheist community needs a diverse offering of groups for the same reason that a restaurant puts more than one item on the menu - more customers or more members, as the case may be.
Another benefit is that diversity allows for experimentation and innovation. Group 1 tries things one way, while Group 2 tries a different approach. Over time, we collect evidence on the merits or demerits of each option.
And while Group 1 may do well in one environment, a sudden shift in the political or social climate may create a situation in which Group 2 thrives.
Finally, a diverse set of groups minimizes the harm done by serious mistake or malevolence. A political or sexual scandal in one group is something that other groups can hold at a distance and condemn, where it deserves condemnation. Let us not pretend that secularists and atheists are always and always will be the paradigm of virtue.
You can explain these facts to the hate-mongering bigot who holds that all "Darwinists" seek the survival of the fittest by slaughtering all competitors, but he will not listen. A person whose interest is in the selling of hate and fear for a profit is not going to listen to arguments that show that their claims are false. The only way to fight such creatures is to get the message to their potential customers.
In the mean time, the best way to proceed is through a multitude of groups addressing separate concerns in new and different ways, but groups willing and able to form a united force against concerns that emerge on a larger scale.