Board Thread:Questions and Answers/@comment-28898329-20160901162911/@comment-27701762-20170107011259

(Also, by "Blank Slate", I mostly meant they were like Flowey was when he first awoke, except we had the ability to keep them from becoming a monster by NOT increasing Chara's LOVE, or turn Chara into a monster by maxing out their LOVE.) But this goes back to my point about Chara ostensibly remembering everything across all of the resets. Chara as "blank slate" can essentially be shown over and over, hundreds and hundreds of times, the importance of friendship and the worth of compassion, including how Flowey reacts to having the ability to feel again, and yet a single Genocide run is enough to turn Chara evil, and permanently evil at that. Conversely, by the same premise, we can perform hundreds upon hundreds of near-Genocide playthroughs, and yet if we end with a TP playthrough then Chara should be good. Perform a single Genocide run, then follow it up with hundreds, thousands, or millions of True Pacifist runs, and Chara never budges from their desire to kill. Taking all of this together, we would need to reach the conclusions that A) Chara is a blank slate, but Toby Fox did not properly formulate the way Chara reacts to the player's/protagonist's choices to showcase this, or B) Chara is not a blank slate.

Finally, though your points are valid, I feel the need to continue the discussion by mentioning that if Chara tried to suppress their depression (such as laughing or smiling it off), eventually, well.... It gets tiring. You can only hide it for so long, and once you stop, the result is often anger. It's a lot of speculation, I know, but if Chara didn't want Asriel to know how depressed they really were, they probably would have tried to act happy, until they couldn't take it anymore, lashed out at Asriel, then, regretting it, commited heroic suicide to end the suffering, in a way that would help the only people that ever loved them....

I originally had a longer response, but for the sake of brevity I'm cutting it down to the core point I want to make. Whenever an explanation is provided for a character's motivation, backstory, etc., there should be some sort of evidence for that explanation, which does not rely on an interpretation of indirect lines. Those interpretations can be useful if there is some evidence that the lines should be interpreted that way, but we need to start with premises and work towards a conclusion, rather than the other way around.

So there is some evidence that Chara was previously evil/malevolent/sadistic/what have you. Asriel tells us that Chara hated humanity, and that except for their fashion choices, Frisk and Chara are nothing alike, with Chara being described as "not really the greatest person." From there, it is reasonable to interpret Chara's laughing at Asgore's sickness as that prior evil/malevolence/sadism.

It is, of course, not the only possible explanation, but if Chara's character is going to be explained through depression, what specific evidence can be brought forward to show that Chara at least may have been depressed? Recall, of course, that we need something along the lines of what we have for the other explanation. Some sort of explicit hint that Chara was depressed. Anything along those lines that makes it reasonable to read that laughter in the way so many others want to: as a sign of nervousness.