Thanks all for the comments. I'm delighted to receive so many.
In case your are interested - maybe some of you know Prague Airport - here is the back-story.
The planned new runway would be to the south of the terminal buildings whereas the current one is to the north, so as I understand it, there would be no need to cross one to reach the other. However the noise issue is that the new runway would bring the trajectory 1.5kms closer to the urban area. The Airport likes to claim that by closing 12/30 it will relieve noise for 200,000 residents but we discovered that in 2019 only 5% of flights used 12/30, whereas 50% of flights would use the new southern 6/24. They have just recently started playing the 'safety' card. One politician last week claimed that it was, in this respect "ordered by Brussels". I'll be on his case!
I am sure it's just a straight business issue, but without any evidence of need. They claimed the capacity would be reached based on growth figures by 2028, but they had no evidence of their own for where this growth was coming from, as I discovered by pressurising them under the Freedom of Info law - the Airport is State owned. I also discovered that Eurocontrol is open and helpful to members of the public who seek help understanding their data. Their forecasts, even pre Covid, didn't support the Airport's growth figures. It looks like a case of "build it, then we'll find some airlines to use it".
I'm a fairly regular flyer (how else would I get back to family and friends in London, especially when i got the call that my Mum had been given 24 hours to live? BA helped get me to her hospital bedside 6 hours after I got the call) and I appreciate Prague needs a good modern airport. But there are other airports in the country which lose money because they are underused, and in regions which need economic investment. And yes, I live in the zone where we would be disturbed by the new flights. But we bought the house in 2002 and as a Londoner of course I tried to do due diligence, with the airport so close, and we were told 'no plans to expand'. Grr.
Basically I supposed that if you guys are happy to fly in an out of Prague, or a similarly configured airport, then the "safety" rationale for a parallel runway is pretty low down the list, and you seem to generally confirm that. For which I, once again, thank you.