Although I broadly agree with the sentiments of the veteran at DFW, the British are a different mindset. Knowing the 'get on with it', almost cynical mood of HM Forces, I suspect anyone doing the same at LGW would be looked at as a bit of a nutcase. Rightly or wrongly the US wave more flags than us and believe mushy sentiments such as 'land of the free, home of the brave', and in many ways that's only ultimately got them into more nationalistic trouble later on!
We're much more reserved and less expressive, as both civilians and service people, and while there probably is the need for a mechanism for the public to express overt support, grannies queuing at Gate 1 at Brize isn't the answer.
Enforced parades isn't it either - certainly not in the RAF, where most people I know would do anything to get out of one!