From An Anarchist FAQ:

Anarchists are well aware of the importance of building organisations. Organisations allow those within them to multiply their strength and activity, becoming the means by which an individual can see their ideas, hopes and dreams realised. This is as true for getting the anarchist message across as for building a home, running a hospital or creating some useful product. Anarchists support two types of organisation – organisations of anarchists and popular organisations which are not made up exclusively of anarchists such as industrial unions, co-operatives and community assemblies.

I.e. there is absolutely nothing contradictory about anarchists seeking organizations.