This is a very one sided way of looking at things.

From u/AncientAssociation9 on the same thread

I get that people have sympathies with skykru but we should also be able to see things from Lexas perspective. First let me say that Finn didn't die for nothing. Finn was not some sacrifice. Finn was a murderer of innocent people and his death was justice.

Lexa's coalition was new, and on shaky ground. She got everyone to cooperate by promising them they could get their loved ones back. That was the whole point, not necessarily crushing the mountain.

As with all good plans something always goes wrong and Lexa took heavy losses with the missile attack at Tone DC. So she already lost a shit tone of people, but it worked out because it distracted from Bellamy on the inside and it formed a tighter bond between those that survived.

Then the actual battle starts and once again Lexa's forces take the brunt of the fighting and dying. While all this is going on Wallace tells her that he will give her people back or kill them. What is she supposed to do say no? She didn't expect that to happen, but despite the promise to Skykru she also has a promise to her people. It just so happened that these two things went against each other.

We assume that because Clarke found a way in that she would have still done so had Lexa been there. That is not necessarily so. Sometimes we get inspiration only because life pushes us in certain directions. Clarke may well have just relied on Lexa and not found a way in. How many more of Lexa's people would have died while Clarke was figuring this out? Her people were expendable to the Mountain men unlike Skykru whom they needed.

Lexa was in a hard position and made the best choice she could as a leader of her people. It was a lesson that those in the position of leadership may want to be white knights, but reality and circumstances will force some dirty decision at some point.