First of all, most ground based large 8 meter telescopes already surpass the Hubble Telescope in resolution (thanks to adaptive optics); the only difference is the Hubble can take sharper images in visible light (as opposed to near infrared).

Now the NGST (next generation space telescope) is suppose to be attuned to near infrared imaging also; yet ground based 8m (and larger) telescopes already do this ! And the ground based telescopes will surpass the NGST in resolution (NGST only has a 6.5 m mirror). In addition the NGST will cost well over $1 billion !, why is NASA wasting money on this telescope, when it could buy 4 or more ground based telescopes that could do the same thing or better ???????? And the ground based telescopes could be easily fixed if theres problems, NGST is unserviceable where they're sending it !

Resolution is not the only advantage of space-based telescopes. In particular, Earth's atmosphere scatters light, which means that the entire sky appears brighter to a ground-based telescope than to one in space. The place where this is most apparent is in long-exposure images, which are necessary to image extremely faint or distant objects. There is a limit on the length of time such an image can be exposed in a ground-based telescope before the objects being imaged become washed out by the brightness of the sky. This almost not an issue for space telescopes, which is why Hubble can produce deep field images (such as these: 1, 2) while ground based telescopes (even those with adaptive optics) cannot.

The other major advantage of space telescopes is that they can obeserve astronomical phenomena at wavelengths of light blocked by Earth's atmosphere. Hubble can see into the ultraviolet, which is largely blocked by ozone layer, while JWST will be able to see a large band of the infrared, significant parts of which are blocked by the atmosphere.

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