So what are your thoughts about this scene?

I must admit the first time I saw it I was a little shocked. It seemed very out of character for Jon,

Then I realised it's just D&D trying to get a reaction from the audience, without caring about character consistency or plot.

Jon is fine with executing a young orphan, but Melisandre, who burned a child alive, is simply banished.

I mean the very fact that Thorne allowed Olly to be apart of the assassination is a tad ridiculous in the first place. Again D&D only care about showing off their actors and getting a reaction from the audience.

Of course Olly doesn't even exist in the books. 

He's a complete invention of D&D.

And how does that even matter? Moron.

Since you're asking how people felt then, I went back into my archive and dug out what I wrote at the time.
The episode aired on 9 May 2016.

A week before, I was writing this:

I was getting very disappointed with the show at the time and not posting all that much. Needless to say, my reaction to that scene was not particularly strong. It was expected, as Jon had to take measures. I liked the way Thorne had been given a dignified departure and thought Olly's hard faced silence had been fitting. Jon deserved that haunting stare. All in all, this 3rd episode was the best of the season, the one least ridden with nonsense and fool pleasing.

Later in the week, on Saturday, I wrote this:

Except it wasn't "comeuppance". Olly and Thorne were right. Jon is an incompetent fuck and his last initiative brought the Wall down.

A matter of terminology. I usually see "comeuppance" used in a general, morally loaded sense, carrying the wish that a bad deed will one day be compensated by some form of punishment, regardless of how related it is to the deed itself. It also expresses that the punishment is deserved. What we have here is a direct reaction. Jon has to kill the rebels in order to re-establish his authority as the one who decides on others. This is basically discipline enforcement.
This is also why I object to his leaving his position afterwards. If his watch "has ended" with his death, as he says, then he no longer is Lord Commander and has no legal authority to enforce anything. Edd will be right in his criticism at the beginning of the next episode: "for this night and all the nights to come". Jon is not free of his oath. He has his cake and eats it.

The terrible thing in the wider scope of the story is that what Thorne said came true: "what he thought was right would have been the end of us".
To this day, there is no indication that the Night King would have had any means of becoming a threat to the south and Jon never had the shimmer of an idea how the wildlings were going to be of any specific help instead of a threat to their winter supplies. Had he sent wildlings on Stannis' ships to go mine dragonglass on Dragonstone, had he trained them to hunt White Walkers with special weapons north of the Wall keeping their families as hostages, we would have a different situation but Jon played the humanitarian, not the tactician.

They pretty much made sure we hated the kid by the time this happened.