Instead of saying "No, you stupid douchebag", why not phrase your argument in terms of "Yes, and..."? Instead of posting screeds about how early employees of startups get screwed, why not phrase it as "Startup founders could solve many of their hiring problems by offering meaningful equity - not just a few percent, but enough that a successful exit is life-changing for all their early employees. This would also fix incentive alignment problems and ensure that employees keep working hard even when they're not in the same room as the boss." You might find some unlikely allies, even among the likes of Sam Altman [1] or Andrew Mason [2].
Or instead of complaining about how Evan Spiegel is an undeserving twat who represents everything wrong with the VC industry, why not highlight the startups whose products you believe are deserving, evangelize them to friends and acquaintances, intro them to people who may help them, and help ensure that the next founder who ends up with a unicorn deserves it?
As you've said before, negative information never gets erased, you have to "flood the channel" [3]. The connection that you didn't make is that negative information (and its ensuing push-back) also reflects negatively on the person who posted it, since most readers are intelligent and can assume that there's more to the story than the side that was posted. Flood the channel with positive information, not negative. You'll find that it becomes much, much easier to achieve your goals.
[1] http://blog.samaltman.com/employee-equity