That pernicious thing called culture
Mona Lisa Smile tackles some big, important questions about culture. Not just the culture of the 1950s - after all, that's kind of an easy target for us 2005ians, ain't it?
No, it should help us to question our own culture. And the very nature of culture. Look at the world portrayed in Mona Lisa Smile - there's no written rule that says a woman can't be a lawyer, can't stay single till she's 40, can't learn all sorts of things... etc.
There's no written rule, but there are all sorts of constraints on real behaviour, based on "what will people think"?
Of course this factor is still in play today. Less so in countries like New Zealand, Canada, Australia and (I guess) the USA - but there are still strong expectations on what you should be.
Are those expectations bad? No. People in general expect you not to go and kill someone. That's probably a good thing (and it's also good that we've internalised this, too).
Culture is neutral. It can be tremendously evil, as in Hitler's Germany or Mussolini's Italy. It can be simply deathly, as portrayed in The Office ("I'm a motivator!"). Or it can be remarkably positive, like... we need a few great examples!
The key is, realising it's there. Realising that there never will be a society where people can do their own thing completely; that there always is the perception of others to be aware of, and use either to your defeat, or your advantage.