Hmmm - maybe I have only had experience with bitter-hopped tins. In these there were no flavour or aroma hops, so there was no concern about losing anything. I brought it to the boil to make sure it was all sanitized, then added the flavour and aroma hops, so in all, a relatively short boil - ie no over-darkening. For these kits, this has worked fine for me.
In the boxed kits that DO have the flavour and aroma hops (I have bought Festa Brew and Brew House), do not boil for reasons mentioned above.
By the way, I am not arguing with anyone - only clarifying my statements and giving them context.
B