Surely you're making the mistake of categorizing the neighborhood, when you should be categorizing the people?
No, Cloudmark specifically said they block or filter Tor IPs because the IPs send them malicious traffic, not because they're Tor.
By comparison: what percentage of the world's SMTP is spam? What percentage of the world's HTTP is filesharing?
About 90% of SMTP is spam. SMTP from Tor nodes is so close to 100% that I don't know anyone who accepts mail from them.
R's, John