This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Terminator 2: Judgment Day
"I know now why you cry. But it is something I could never do."
Doubles as in-universe tearjerker: Sarah harshly Complaining About Rescues They Don't Like when she reunites with John, who was expecting some warmth and affection, but is instead devastated by her callous response.
The novelization takes it a step further; Sarah has been desperate to toughen up her son, to prepare him for the war to come, but seeing the hate in his eyes after brushing him off, she laments at how much this whole mess has cost them.
John and the T-800 watch a couple kids play with toy guns:
"We're not going to make it, are we? People, I mean."
As Sarah Connor was about to murder Dyson in cold-blood in front of his family, she realizes that she has become exactly like what she hates the most, and collapses weeping in guilt.
Sarah is trying to steel herself in killing Dyson by shouting, "IT'S ALL YOUR FAULT!" Dyson, bleeding from a previous gunshot wound innocently utters, "What?" He was about to be killed in front of his family and he honestly does not know why.
Sarah's summation of the Terminator; how despite or even because of its inherent inhumanity, it is the perfect father figure for John. Now think of how it sacrifices itself in the hopes of preventing Judgement Day. Sarah's life was forever changed by the few days she knew Kyle Reese, and John's was equally changed by the few days he knew the Terminator.
Watching John with the machine, it was suddenly so clear. The Terminator would never stop, it would never leave him... it would always be there. And it would never hurt him, never shout at him or get drunk and hit him, or say it couldn't spend time with him because it was too busy. And it would die to protect him. Of all the would-be fathers who came and went over the years, this thing, this machine, was the only one who measured up. In an insane world, it was the sanest choice.
The "burning playground" opening, juxtaposed to Brad Fidel's gentle and heartfelt rendition of the "Terminator Theme" strikes just the right emotional nerves, reminding us of how important it is to save this world for the next generation.
Hell, this entire sequence is a Tear Jerker. It's VERY heartrending to see John pleading the T-800 not to go. Even after you consider that it was the closest he ever got to have a father figure. Doubles as a Heartwarming Moment, when watched back-to-back with Sarah's final speech in the movie.
The Final First Hug between the T-800 and John is pretty heartbreaking too.
The T-800 and Sarah are both being The Stoic, as they know that this has to happen in order to prevent the creation of Skynet. John, however, simply descends into Inelegant Blubbering that leads to a truly heartbreaking Heroic B.S.O.D.:
The look on Sarah's face right before she hits the button to lower the T-800 says it all; from the moment she first saw it, despite the fact that John's survival was its mission, she hadn't trusted it, all but vowing to destroy it at the first opportunity. Now, in the end, she has her chance....and she clearly doesn't want to.
Sarah's last line from the film:
Sarah: The unknown future rolls toward us. I face it, for the first time, with a sense of hope. Because if a machine, a Terminator, can learn the value of human life, maybe we can too.
What makes it especially sad, was in the original timeline before Skynet's meddling with time travel, John never reconciled with his mother. He hated her... until the nuclear war she spoke of happened, and the survivors faced the nightmare, of the war against the machines. Cast your mind back to the first film, where Reese memorized a message for her... that she was his source of strength and comfort during the dark times. He deeply regretted never believing her again after she was incarcerated.