It's not that you can't it's that your stake can be countered and your vote causes conflicts within the community when you're unrealistic about the value of your friends posts.
You're not looking at the bigger picture. If you're not voting in a manner than makes the platform attractive to the outside world then you are causing damage to your own investment by voting in your self interest (which in the long run is not in your interest). Nepotism within any community is unattractive.
And the last reason to invest would be to protect an investment we have not yet made so the argument that anti social voting behaviours increases demand is just ludicrous.