It's an appalling decision that will completely wreck an irreplaceable green space (and historic park) in the heart of London. This is of course deliberate

BBC:

Architect Sir David Adjaye, who has led the design team, previously said "disrupting the pleasure of being in a park is key to the thinking" of the memorial.

From the same article:

In a letter to the council, Royal Parks said while it "strongly supports" the principle of the project, it thought the current design would have "significant harmful impacts" on the "character and function" of the park.

"The structure will dominate the park and eclipse the existing listed memorials which are nationally important in their own right," the charity said. Royal Parks added the number of visitors expected would create "queues and congestion" and "change the nature of what is currently a relaxed park".

The Save Victoria Tower Gardens protest group points out "this plan will change forever the use of a much loved and well-used local park into a sombre, security patrolled civic space" and that the holocaust is already memorialized at the Imperial War Museum, less than a mile away.