I can confirm that the Forest Hill Society has submitted an objection to the Tyson Road development, not because of the traffic issues associated or because the density is too great, but that the density levels is not suitable for the location, results in bad design, and inconveniences many local people permanently. I find this a very different situation to a single event per year.
You are right that I was not personally effected as I was enjoying the day at Horniman. However, I know plenty of people who were badly effected in a variety of ways. Despite this most I have spoken to in the local area support events in Horniman, as do 40% of people who voted in the poll (for what it is worth).
I am sure that the organisers are quite capable of looking for another location if they feel that the Horniman is too small, they do not need me or you to do this for them. However, if they do wish to continue in the Horniman then they will need creative thinking and possibly the assistance of local people to make it work. Whilst I understand your concerns I would prefer to work at ways to resolve them inside Forest Hill rather than outside - is that really so awful?