"Why would someone send money to a fund-raising address if they didn't want to participate? If they are paying the person, they would not use the fund-raising address."
Is there anything that prevents a fund-raising address from being used for something else as well?

In the long run, wouldn't it be better for Simple Send version 1 to become Send with a Type/Reason field indicating "Simple", "Investment", "Restricted", etc rather than creating a new tx for each new reason to send?