Irresponsible not to test?

I see a lot of people saying they won't test/didn't test for things like chromosome disorders, and so I was wondering what people thought about this? Is it irresponsible not to test? Some people say they don't do it because the results would not make a difference to them and they would keep baby whatever, but personally I think it's better to know so you can prepare for any issues you baby may have. What do you all think?