If it's a default response for you (the generic you, not you specifically) to say it rather than think through the problem...I mean, that says a lot about societal awareness, and I can't really find much sympathy for that, but you're right in that some well-meaning idiots might view it as a surface-level thing. But those well-meaning, superficial people aren't in the discussion in the first place. Even Hillary Clinton--who should have known better--isn't going to BLM events explicitly as counter-protestors to chant "All Lives Matter" at them. Right now, as 2016 opens, "All Lives Matter" is the dog whistle of dog whistles.