Threatening to leave an organization if you don’t get your demands met is an inherently risky strategy.
The best case scenario is that your demands are met and you gain a reputation as the sort of person who delivers ultimatums.
If you don’t get your demands met, you must follow through with your threat to leave or you’ll gain a reputation as the sort of person who makes empty threats.
If you leave, you’ll cease to have a voice in the organization’s affairs. If your threat was part of a campaign of like-minded people, unless they are a large enough block that the absence will materially impact the organization, the walkout will be little-remembered and have little effect.
If you still want to try such a risky strategy, a couple things will help you be more effective.
First, make sure you’re actually part of the organization. Threats to leave from people who have never joined are not very persuasive, though do add a nice touch of humor to the recipient’s day.
Second, make sure you have built a reputation as someone valuable to the organization. If nobody knows who you are or can figure out what your contributions are (or worse, knows you very well as the person always complaining), they are less likely to consider your departure much of a threat.
Hope that helps.