He was a man of his time. All of the books I've read of the era talk about corruption as part of doing business. Many of the things we consider corrupt now where very legal at the time. The Standard Oil monopoly was legal at the time. It's not an excuse but you can't exclude it when evaluating his actions. At the time he was just being a smart business man. He was no saint but it's possible to learn from what he did.

It's interesting to note that one of the biggest criticisms about him was that he would force companies to sell themselves to him or be put out of business by his monopoly power. Now, 100+ years after, it's still a business practice. I know it happened when Amazon bought diapers.com. Amazon threaten to start it's own diaper service and put them out of business, if they did not sell. Was it a smart business practice from Amazon's view or was it corrupt? I guess it's up in the air since it's still happening.

If you read Teddy Roosevelt's bio you get a view of what politics and business where at the time.