Adding a team to catch up

If a project that consists of 2 teams is behind, it makes sense that adding an additional team would help catch up, at least on the surface.  The comments I am getting back are, that adding additional people to an already existing team could disrupt the team and actually cause them to be less productive.  I get that.  But wouldn't adding another team be a reasonable solution?  I thought that one of the benefits of scrum was scalability.