What is the meaning of the strong man is strongest alone

Most of the time, when you have a strong man, that indicates independence and a strong will. Strong willed people tend to stick to themselves and take care of themselves BY THEMSELVES. That's one translation lol

2. He fears for Goodman’s safety in the mob.

Explanation:

In Rod Sterling's "The Monsters are Due on Maple Street", the most dominant theme is the upheaval and disorder caused over the issue of an alien invasion over maple Street. The eventual fighting and 'revolt' against one another in this neighborhood was the proposed plan of the alien all along, who are intent on invading the earth, one neighborhood at a time.

The given passage is from the scene where the neighborhood "oddball" Les Goodman's resides. Due to his weird behavior and "insomnia", he was suspected of being the alien among them, sent to spy. So, when the group of  people decided to approach his house, Steve tried to make it look less scary for he believes that they are wrong in making false accusations against anyone just because of Tommy's stories about alien invasions. He tries to relax the 'increasing' anger of the people while also thinking about the safety of the wrongly accused man Les Goodman.