"building orbital telescopes"

Do you realize the cost of these things? And how much can be achieved with normal telescopes for a fraction of this cost? It's like saying we won't build bridges anymore because we have planes.

E: grammar, a little bit

Kessler syndrome does still apply. There could be runaway collisions and impassable debris in low earth orbit for 5-10 years before enough of it burns up, putting all that metal into the atmosphere.