I think everyone knows he is today branded as an unmitigated racist. So, because my nature is contrarian, I offer the following in mitigation--
1. Yes, he probably was racist. But when MLB was integrated in 1947, Boston was a very racist city and continued to be so for many years. Don't take my word for it, read what Bill Russell used to say about Celtics fans and Boston when he was here, 1956-69. He did not hate whites per se because he admired and liked his coach, Red Auerbach, and the owner, both white. He hated the racism of Boston, however, and was quite vocal about it.
2. And don't just take Russell's word for it either. Look at the attendance figures for the racially enlightened Boston Celtics during the Bill Russell era when the Celtics won 11 NBA championships in 13 seasons, by far the most successful run by any major sports franchise in the history or American sports. During that run they never sold out a single game in Boston Garden, seating capacity 14,000 (13,909). Their best season in the Russell era was 10,517, which was also the first season they ever won the NBA championship. By 1961-62, smack dab in the middle of the Russell era, the most successful in professional American sports history, it was 6,852, which was less than half of capacity. In 1955-56, the season before Russell arrived, attendance was 8,063.
3. Then there's the Branch Rickey-Jackie Robinson saga taking place in Brooklyn and the National League. Anyone remember the movies about Jackie (there have been at least two)? Almost everywhere Jackie played he was subject to abuse because Boston was not the only racist city in America. Just about every city was, and the fans (some of them) made that abundantly clear.
4. Then there's the issue of what form Tom Yawkey's racism took. To read some of the commentaries, you would think he was a slave owner or regularly throwing African Americans in jail or at least putting a big dent in their chances for employment.
5. Well, not really. He denied excellent baseball players employment with his ball club for 12 years (1947-59), but it was a small part of the whole and actually didn't prevent those very few African-Americans from playing for other MLB clubs.
6. Plus this. Roughly three years after MLB was integrated (and so were the Minors), the Negro Baseball League, "among the largest and most prosperous black-owned business ventures, were allowed to fade into oblivion." This is not an argument that Yawkey was doing a good thing by not integrating the Sox, but does say it wasn't quite as harmful as has been claimed.
7. Yawkey bought the Sox in 1933 when their average game attendance was 3,732. The very next year it more than doubled to 7,930, still far short of the 33,000 capacity, however. The next big jump came 12 years later, 1946, the first season after World War II, when attendance shot up to 18,166 per game and stayed that way for 4 seasons, then ground slowly down and stayed there thru the 1966 season when it was 10,014. Then came 1967, Yaz, etc, and attendance more than doubled to 21,000 and basically stayed close to that until Yawkey died in 1976 (attendance that year 23,406). He had his faults as an owner, but was still better than those who proceeded him.
8. Meanwhile, Boston itself was changing demographically. In 1940 it was 97% white, and in 1970 it was 82% white and in 1990 it was 62.8%, about where it is today. I think we can assume that attitudes have changed with the demographics. Heck, Bill Russell has even deigned to return. And word is that during his later years Yawkey got along quite well with the African Americans on the Sox.