Biking does take the impact off the feet and knees. Running is a high impact sport, no doubt about it. But destroying joints isn't solely about impact, it's more about biomechanics and what you do to correct biomechanical inefficiencies. A pair of shoes that fit my biomechanics that was replaced when the foam was worn out has gotten me through 11 years of running, with the last 6 at 70+ miles per week and the last 2 at 85+ miles per week with very few injuries.

It's not about having an opinion, because how much stress a given sport puts on your body has as much to do with opinion as someone having the opinion that 2+2=6. It's funny...I've had a lot of running teammates over the years who say they've only had knee problems when cycling. Their argument is that turning little circles is an unnatural motion and the high rpm wrecks their knees. And I've talked to a lot of sports doctors who said the exact same thing. But then you check their saddle height and give them pedals with more float, and they're usually alright (unless they had a preexisting knee condition, either from running or cycling, that was exacerbated by the particular stress that cycling puts on the knee).