By the definitions set out in the core books (and there are just three of them) alignments are not some philosophical discourse, they are tangible and have direct effects and meaning in everyday life. Which is precisely why you can detect them. Or build swoards that harm people of specific alignments. Or restrict who passes through an enchanted gateway by alignment.
The cannon response is that they are evil. Born that way, can't help it.
For your own campaign, you might rule zero it one way, the other, or both, depending on the circumstances, and that is entirely fair, so long as your players are given enough information to know how their culture stands on the issue.
Another cultural consideration for you to chew on is the actual view of kobolds held by the player's society. Are kobold sentient creatures gone wrong, or are they monsters, abberations, demon spawn beasts that need to be slaughtered en masse?
If it's the former, there may be some ethical issues with genocide. If it's the latter, killing a kobold whelp to protect a town is no different than killing a wolf cub to protect a flock of sheep from future predations. IE: If you reduce them to animals, it's a very easy case to close. If they are "beings" and acknowledged as so it becomes an entirely different ball of wax.
A very good twist would be to have the culture view them as beasts and animals, undeserving of anything than a quick slaughter. Then present the PC's with a situation where a kobold mother is trying to protect her young and appeals to the party to "let us go away from here." as a sentient thinking creature.
If they embrace their culture, they slaughter them anyway. Just a bunch of animals. If they accept the kobolds as thinking creatures, it changes how they interact with them from that point forward.