cruising is a clear matter. you see when someone is cruising - and sometimes you even hear it. - now thrusting is different. ... for example, what when two fighters are thrust / E-killing and jousting? ... their relative speed toward each other is 400, and they quickly have quite a distance between each other.
but then, which of those is retreating when the distance grows too much? - both of them may still be E-killing in opposite directions.
so the cruise is different to thrusters. - but the point is not that some people do it - or that some people think it should be OK to do it. the point is - if you want to be on the safe side, you just don t cruise in pvp unless you want to flee. cause for all you know, the other person may place a sanction on you if you cruise to catch up - and no one wants that on him, no matter how much you argue if the situation just asked for it.