Your beacon target is part of your assignment, whether it's spoken or not.

Similarly, helping your fellow healer, especially if you can see they need it, isn't sniping.

If the Resto Druid is supposed to handle "Blank Debuff'" and they're doing fine at it, but suddenly you get two or three "Blank Debuff"s instead of the normal one because DPS was dumb or you were just extraordinarily unlucky (it is possible in some situations, although rare), helping them because you easily can thanks to Beacon isn't sniping. It's being nice and contributing to doing the encounter.

Doing "Blank Debuff" for them every time, regardless of Beacon, would be sniping. Beacon just makes it easier for you to do it without being caught/without slacking on your own jobs/with "an excuse".


Sniping is a grey area in general though... sometimes it does happen, absolutely. But sometimes you can argue you shouldn't have been able to beat the person to it, or it's better to not let the guy die than to assume they'll do it (maybe they sneezed/didn't notice/were being bad/etc) and waiting just increases risk, or that you were just trying to help on a difficult fight... but regardless of that, it's certainly something to keep in mind as a possible explanation, especially when the person's attitude supports it (I've played with a horrendous (to the point of nearly letting his own assignments die constantly) sniper, and his out of raid attitude (somewhat supported or at least not tampered by some literal relations within the guild) made it inherently obvious that it was on purpose and it was to be a smug douche).