For example air pollution levels around LHR are are obscene and cause a real effect on people's health, including many premature deaths. I'm sure if terrorist incidents were killing people every year in the area you would take notice, so perhaps that should make you think too. Unless they can sort that out I think they should proceed very cautiously with expansion.
How much of that population density near the airport was developed after LHR was established as the primary airport in the 1940s? (im honestly asking, i dont know.) if it was significantly developed after the airport, then blame the developers and people who chose to live near the airport, not the airport itself. If, not then you have a very valid point, though nothing wrong with valuing health above expansion, my point is for many living near major airports, it was a choixe made knowing the airport was there. Also, whats the better alternative, expanding LHR or subjugating another area to a newly built airport? Personally i cant stand whining about something that already existed when a person chose to live near that place, which is very common here in the US.
Edited for clarity.
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