This is a good question. Although Atticus's decision to defend Tom Robinson is a highly unpopular one among the majority of the white population of Maycomb, it probably does not affect the specific aspect of his character that is mentioned in the question: respect. Many white people in Maycomb are angered that Atticus has taken the case because, as one member of the Idler's Club states,
"... but Atticus means to defend him. That's what I don't like about it."
The man knows that Atticus will not just go through the motions as a court-appointed public defender might have done. Atticus is even able to sway one of the jury members--a Cunningham, whose kin had confronted Atticus with the lynch mob at the jail--who holds out for several hours before finally siding with the other jurors. Perhaps there is no better example of the respect that Atticus commands in the community than his repeated elections--always running unopposed--to represent Maycomb in the Alabama legislature. No one else even bothers to run against Atticus--a sure sign that even his detractors recognize he is the best man for the job.
As for Alexandra, she commands the respect of many of the women in Maycomb--the Missionary Circle, for example--but she fails to earn the respect of Jem and Scout, who live in the same household. As a woman, she is still considered a second-class citizen in Maycomb, where woman do not hold the same rights as men; and few of the men of Maycomb hold her in higher regard than her brother. Atticus may not be the best-liked man in Maycomb, but he is certainly the most respected.