To persuade my audience to give blood and to support the Wilderness Society is a poorly phrased specific purpose statement for a classroom speech because

It contains two unrelated ideas.

Explanation:

Unrelated ideas are ideas that make no sense once put together. The Wilderness Society, at first glance, has absolutely nothing to do with donating blood. Therefore, it would make for a poor statement to support donating blood. What should be done, is to replace that statement with the institution, organization, etc, that actually receives the blood donated, give more information about how it would be to donate, where does that blood goes to, how many lives could be saved, information about the body process after donating, etc etc.