So, if I'm hearing you correctly, you're saying they purposely meant for a lawful good character to be a mass murderer because they thought it would be funny?
The POINT is that the game was designed so that players would play the game as intended. Lawful Good characters were not MEANT to be murderers just because it's hilarious.
No, you again miss the point. If changing your alignment as a result of your actions should not be possible, then the hell trials in BG2 don't make sense. If changing your alignment should be possible, then it doesn't mean it was done in one step. An LG character can be for example consumed by getting vengeance for Gorion and as a result if that overwhelming hatred can slowly give in to the taint. They don't become the next lord of murder overnight. But in BG1, they cannot become that at all; quite ironic, considering the subject of the story. What is even the point of all those dark dreams and powers?