Railguns are great if you work to their strengths, namely high ship speed. A railgun is already almost as good as a turreted laser at PD, but when you increase ship speeds they rapidly become superior - without having too worry as much about 4x tracking speed. Additionally, higher speeds work to offset their range disadvantage.
10cm railguns are a little exploitable too, you can make truckloads of them for very low cost while still being effective point defense. YMMV, of course.
