<<The income from visitors would more than pay for any and all security requirements and costs.>>
No way, I fear. I mentioned elsewhere that I often saw the viewing terraces on QB and T2 at Heathrow almost devoid of visitors. Back in the 50s and 60s the place was teeming, but aviation nowadays is a fact of life and does not hold people in awe. How many people stand on bridges over the M1 watching cars? Space at airports is at a premium because our airports are so small.