Just like food safety regulation: sure, a company that sells deadly products might not satay in the market very long, but it's going to be a small comfort for those that die from its products before its reputation is touched... In the long run, we're all dead. John Maynard Keynes
His support was instrumental in getting Congress to approve cuts thaty many of them were wary about.
And his responsibility in propping up the bubbles in the late 90s and then throughout the noughties (denying that there even was a bubble, and keeping Fed rates absurdly low for way too long) cannot be overstated.
Quite simply, he behaved like a hawk, and used his "credibility" on the markets (earned thanks to his frequent use of the "Greenspan put", ie using monetary policy to prop up markets when they went down) for narrow political goals. In the long run, we're all dead. John Maynard Keynes