At best those ads simply blend in with all the other similarly worded ads. At worst they ignore the simple truth that, however sentimental we may prefer to be, volunteers come to you because of something they want, not something you want. The key to successful volunteer recruitment is figuring out what you have to offer the volunteer and selling it. Try to find something unique about your organization. Then make sure you mention it prominently in your recruitment message.
Nothing makes a prospective volunteer feel less needed than being strung along.