Unfortunately, many in Maycomb assume Tom was running away. They believe that it is typical of blacks to run away from their problems. Some just assumed that Tom was stupid, because he knew he could not get over the fence.
It should be noted that if Tom had not been crippled, he would have made it. Tom was not running away from his problems, he was committing suicide. By doing so, he was sparing himself and everyone else months and years of pain. It is true that Helen was left a widow, but Tom likely figured that it would be easier on her to have him dead than to have him in prison for life or executed.
Tom ended things on his own terms. He had little control over his life, but he was able to take control over his death. No one could take that from him.