Not have a leg to stand on

http://www.theaustralian.com.au/business/wall-street-journal/agitating-holders-unlikely-to-get-quieter/story-fnay3vxj-1226239609805
“Their role is to preserve and create value but they also need to make sure their value proposition is understood by stakeholders so they have a leg to stand on if an agitator comes along and their value message is something they should be consistently communicating to the market,” Ms Wiggins said, acknowledging having a running start to defending value would be easier than from a standing start.
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Should "have a leg to stand on" be used with such negative word as "not"?

http://www.ldoceonline.com/dictionary/leg_1
not have a leg to stand on
informal
to be in a situation where you cannot prove or legally support what you say:
- If you didn't sign a contract, you won't have a leg to stand on.