Aside from an episode of Strange New Worlds (and possible in Wrath of Khan, depending on your perspective), space pirates aren't brought up as a risk to the Federation starships, presumably because they usually aren't. Shields alone should be sufficient for debris and asteroids, since shields appear to stop physical objects as well as certain forms of energy (obvs. not certain bands of light though, or whatever bands their sensors use). Non- and quasi-sentient species shouldn't pose any risk to a starship at all (aside from possibly omniscient comets, thank you Stanislaw Lem). The weapons on a starship are appropriate to direct against planetary settlements, bases, and other starships.

Fundamentally, I believe Mao was correct on this; the ability to use violence effectively is the lowest common denominator for all power. Everything else is a veneer of civility intended to disguise the violence that is inherent to all forms of coercive rule.