What about those 75 Million $ just to re-enter it? Why not use them for something else, then (like testing the LSAM rocket engines) ?

The HST is orbiting the Earth above a small fraction of mankind (unlike the ISS).
When Columbia returned back, it was still intact at 60 km height, completely above land and yet, when it broke up, all the pieces returned back on land (and no desert) and nobody got hit, even indirectly.

If the HST returned back uncontrollably, it would desintegrate much higher than Columbia, above what is mostly water and if it is land, then it's mostly very scarcely populated.
There are far more chances for somebody to find HST pieces, sell them as relics than there are for somebody to get hit by the HST.

I can very well understand if the HST isn't upgrated, then it will be caught up by more recent telescopes.
But if there is some kind of law forcing NASA to launch a rocket to dock with the HST only to slow it down, then it's more absurd than the law preventing NASA from paying the Russians for the use of Soyuz spacecrafts.

Raoul