Depends on the nature of the man. A certain amount of envy regarding a sibling who has achieved high status and prestige is understandable. But for that to consume your whole being and twist you into someone bent on their downfall? Hmmm. Unless Jim seriously aggrieved him in the past and as a consequence stuffed up his own chances of success, I don't see a plausible motivation.
Hell, I say ride on the coattails. Jim Kirk saved the planet
- and he's your brother! You could have a bevy of hot chicks wanting to nail you as the next best thing to Captain Fantastic himself!