Blue dot and defensive mode are not the same, and neither are red dot and offensive mode.
I'm always in offensive mode, and almost always blue dot (I 'never' (more or less) shoot first).
I don't think you can be red dot and defensive, but aside from that, dot colour is not a signifier of offensive/defensive but rather of hostility level.
But yeah, even in defensive mode, if you get some pesky outlaw with a rolling block or similar rifle, and you happen to be standing still (fishing, for example) he's going to be able to pick you off at long range.