Alternate Character Interpretation: According to spark notes, Tom was attracted to Laura, and felt shameful about it. The reason he tried to prevent her from working was that he wanted her all to himself. This shows up in the movie.
And, of course, the idea that Tom is gay and unable to deal with it in his oppressive home situation. And naturally, he's attracted to Jim. The 2014 Broadway staging takes this interpretation. (Plus, the director, John Tiffany, and Tom's actor, Zachary Quinto, are both openly gay.)
Moreover, some people have estimated that Laura may have some sort of anxiety disorder, notably social anxiety.
Tom probably has social anxiety as well, just to a much lesser extent than Laura. In fact, this is a far better (and more likely) explanation of Tom's behavior than an incestuous infatuation with Laura: Tom is reluctant to help Laura is because he would have to confront his own anxieties. Given Amanda's delusions about how the world works, it's no wonder she raised kids with poor social skills.
Jim could be a genuine, well-adjusted Nice Guy who happens to fall in with a dysfunctional family, or he could be an Amanda-in-the-making, a popularity-obsessed grinner whose best days are behind him and who will happily adopt any illusions to maintain the contrary.
If you look at it this way, in Tom's perspective, it seems like Laura and Amanda's roles in his life are completely reversed. Tom and Amanda bicker and talk like a brother and sister would while Laura has more of a motherly aspect about her and usually tries to encourage the two to make up. Tom seems to be more considerate of her than of Amanda, only doing things so that Amanda will get off his back.
Award Snub: It never won or was even nominated for a Tony Award until the 2014 staging. Even then, it only won Best Lighting out of the seven awards it was nominated for, despite universal acclaim for the acting.
Genius Bonus - on the screen that is projected on the back of the stage (optional) one of the first words that are flashed up is "Ou sont les neiges d'antan?" Meaning, "Where are the snows of yesteryear?" this refers to an old and classic French poem mourning the loss of the great beauties of the world.
Tear Jerker - When Laura's showing Jim her glass unicorn, she's so happy — like she's just so happy someone's listening to her and caring what she says. And then it breaks.
The Woobie - Laura. She never hurts anyone else, and all life does is knock her down.
What Do You Mean, It's Not Symbolic?: When Laura's favorite glass piece — a unicorn, that longtime symbol of purity and rarity — that she showed to Jim breaks. Even more so because it breaks off its horn: "Now it's just like all the other horses".