In many respects, the argument between Tom and Amanda in the scene is a result of latent tension that percolates to the surface in the scene.  Amanda's insistence on Tom being a more present in the home has grated on Tom's nerves for a while.  She cannot understand his own desire to have freedom or his own life.  At the same time, perhaps, she chooses not to understand his own condition and his own desires, as it might be reminiscent of Tom's father/ Amanda's husband.  On the other side of the argument, Tom is looking to escape, bound in the family only by a lost sense of duty.  The argument about Tom going to the movies is where the crux of this debate lies.  For Tom, it is what he sees as freedom and escape.  More importantly, it represents his first steps towards leaving.   Amanda sees it as self indulgent and narcissistic.  The implication of Tom's deception, lying about him going to the movies, is also what fuels the intensity of the argument.  Williams also uses the fight to begin the process of separation between Tom and the family.  The magnitude of the fight represents a line that has been crossed in which the reader/ audience sees that the relationship between Tom and Amanda might lie beyond repair.