When comparing the man's legs to rubber in context, it sounds like he is unable to walk. Describing his legs as rubber would indicate they bent and bowed under his weight on them. He's probably either injured or lame.
Taking a position in an argument means taking a side. When taking a side in an argument, the author will most likely give you biased evidence. They will only give you reason to believe their side, without giving you any sort of evidence for the other side in the argument.
I hope this helps!
