Monkey D garp and marines

[Robin]

D is said to be the death and doom of the peace and countries and such. So, people who have the middle name is "D" are feared and they are not welcomed in any part of the world. So, how come Mokey D garp is the vice captain of a fleet? 
Isn't he a significant threat too? If you look at it closely, it is obvious that he let luffy beat him during ace's rescue to save ace.
So, he might not be a fully dedicated marine at heart.

What do you think?

 

[Blackangel]

i don't think garp is very powerful and he failed to protect ace and he himself wanted to execute ace which is very heartless.
i don't like garp but he not having a tough time in marines