Well I suppose you're right in that quite a few areas across London have been designated for growth - Vauxhall/Nine Elms, Elephant & Castle, Stratford, Old Oak Common etc. Higher densities in these areas are supposed to be the most efficient and sustainable use of land, aided by good public transport accessibility and helping to deliver the extra homes London needs. The intentions are good but the delivery has been patchy to say the least.
Part of the problem is people don't like change, and particularly on the scale seen in Vauxhall. I'm not at all keen on what has happened there due to the mish mash of design and heights, but the drivers behind it are sound even if the execution of it has been all over the place.