The implications are important, yes. The action itself is not, it's a reflex of Shepard, who's on adrenaline (hence the railroading), not something he thinks about. It's not like he stands there for a moment, deliberates all the consequences and then acts, he does so immediately.
The action itself is, indeed, important. Had Shepard smartly responded to the scenario by letting it play out and safeguarding the other soldier or reflexively lunged the affected party out of the way, we'd have entirely different circumstances. We don't, because Shepard ran into the impact zone, moved in front of the beacon's energy, and threw K/A away in creation of a situation where they effectively took their place.
I'm not really in the mood to get into a discussion about whether acting on reflex is considered a conscious decision or not. Either way, whether it's considered a choice or a reaction, it's beyond the player's control and an inbuilt part of Shepard's character.
We are armchair interpreting the living crap out of something that happened in literally a few seconds. It's ridiculous.
No need to be derisive. It's a significant moment for the trilogy, both in terms of the plot and of Shepard's innate characterization that the player cannot avoid. Monumental things can, and do, happen in seconds. They can make or break what kind of person an individual is, or isn't.
If you want an example, Shepard saving Joker at the beginning of ME2 might be a better one, even (although, even there, I don't think Shepard planned on getting spaced either but at least there, the entire process is long enough for Shep to be fully aware of what he is doing.)
So "suicidal Shepard" is accurate in ME2 as well?
"Suicidal" isn't really the right term, but yeah, BioWare imposes their canon on Shepard in the intro Normandy sequence as well.