I have also herd this many of times.
What people don't think about is the technology we posses in this day and age,
if a meteor was about to strike earth, we would know about it well before it got near the earths atmosphere, as their are observatories round the globe studying the sky's and the space around us twenty four seven.
I'm sure the idea of diverting mass would work, what i mean by this is... landing shuttles in a certain area aboard the meteor/asteroid, then having them all fire afterburners and multiple jet powered engines to divert the meteor/asteroid to change its course, the best way to do it would be to send it sideways to the bearing it is headed as sending it back the way it came would take more momentum and fuel, witch we might not have when using a lot to get there anyway.
(I don't see how this would work though as oxygen is needed to create a flame, but oxygen tanks could be used to coincide alongside the fuels needed to create a combustion chamber.)
When and if it comes to the time of a meteor heading for earth, evasive action would be taken in the quickest most life conserving way.
Worry what you will, as it will only do you no good if the inevitable does happen.
As for me,
If the world ends.... I don't give a toss as i will have lived the best years of my life by then.
