In To Kill a Mockingbird why did Jem destroy Mrs. Dubose's flowers? Do you think his punishment was fair?

On the way to town that morning, Jem and Scout had passed
Mrs. Dubose's place, and she was sitting on the front porch.  As they passed, she
starting hurling insults at them, criticizing them and Atticus.  She was pretty rude and
caustic; one of the remarks centered around Atticus being a "nigger lover," for taking
the case of Tom Robinson.  Jem was furious.  Normally, he took her comments in stride
and brushed them off (she always insulted them when they walked by), but that was too
much for Jem.  On the way home, when she was inside, he destroyed her flowers in
revenge.

Atticus made him go to her house and read to her
every afternoon until she died.  It was an interesting punishment, to be sure.  It might
seem a bit drastic, but Atticus was trying to help Jem to see what a strong, "brave
lady" she was as she fought against her addiction.  Atticus was all about seeing beyond
people's exteriors, and looking at them for who they were on the inside, and that is the
lesson that he wanted to teach Jem.

I hope that helped;
good luck!