An IllegalArgumentException is produced when loading MavenFacetInstallPage when the jst.seam facet is missing. One should be able to install the m2 facet regardless of whether or not seam tooling is installed.

This is the line where the exception is thrown:
public static final IProjectFacet SEAM_FACET = ProjectFacetsManager.getProjectFacet(SEAM_FACET_ID);

This should be moved to a static init block to either catch the exception or check to see if the facet is defined first.