It's a pretty basic tenet of airport design that one should not build them where there is an identified, and impossible to manage, safety risk.

If you want to ignore that and risk people's lives for convenience, then so be it. We got our lucky break on the Hudson. I've read the transcripts from planes which crashed as a result of hitting birds, in which everyone on board was killed and I cried as I read them. I've met survivors of crashes due to bird strikes. To deny the very real risk that a estuary based airport in the Thames would have is to put your head in the sand and hope that neither you, nor your loved ones, are killed when the accident happens.