The original blame lies with Bristol City Council or Bristol Corporation as it was then for deciding to buy Lulsgate instead of moving to Filton in the 1950s when Whitchurch became too small - we seem to have come full circle.
Tenancy of Filton was reputedly offered at a peppercorn rent but the council would have been tenants of the BAC as the owners and occupiers were in those days. Perhaps that's why they didn't want to move there though there were so few flights in the 1950s and 1960s from Lulsgate that being a tenant at Filton would not have been a problem, surely.
Bae were the owners of Filton by the 1990s and in the middle of that decade applied to use Filton as a city airport. A public enquiry was held after which the relevant government minister (it was a Conservative government and I believe the minister was one J S Gummer) rejected the application. I seem to remember an appeal, or at least a judicial review of the minister's decision, by Bae to the courts but that too was rejected.
It's true there are many more nimbys around Filton than around Lulsgate - the much larger population there makes this no surprise.
Lusgate is the only game in town now even though with hindsight, and certainly prescience on the part of the city councillors (something of an oxymoron when applied to Bristol councillors) all those years ago, Filton would now be the airport for Bristol - no environmentalists or professional objectors in those days.