You can build AP support with sightstone, it is a viable build. If you are by any chances a type of people who see supports like Annie, Karma, Lux, Vel'koz, Zyra and flame them for building AP after SS, you are doing wrong.
Supports should build sightstone most of the time and they shouldn't take cs unless adc is at base and they are just last hitting. But don't confuse softening minions and helping to push with taking cs. Lane control is something that is severely lacking in bronze and silver. If your support hits minions without killing them, don't flame, ask what is he doing. In bronze he can be last hitting though, then you are right.