Sutra, Tantra and Ati

Always wondered why more mystically inclined people don't just come out and say that "There's only God." The basic idea that there's only Ati has been around for a long time. However, whenever I mention this to friends and colleagues who meditate, go on retreats etc., I often encounter a somewhat embarrassed about take---as though this particular statement is too simplistic. The same people are also more likely to expound on "no self" or "Atman" or "Spirit" or whatever and often in a very intellectual way. Perhaps, "There is only Ati" implies a commitment to idealism---I don't know---but I don't see why it should.