Should be able to gift the core game
HoT isn’t a bundle. The core game isn’t actually included with it. HoT’s serial key simply grants full access to the game. If they were going to allow people to give away the core game, they wouldn’t have included it like that, they would have sold it separately.
If someone wants to try the game, buy it from buy.guildwars2.com, then request a refund through support. You have up to a month to request a refund, though do note that the account will be permanently banned, including the email.
In the near future however (after HoT), there may be actual trial accounts.
That would actually defeat the purpose of giving the core game for free. If the intention was to limit the division of the player base for new players, then adding more players which would be limited to the core game would further that issue.
The perception is that ANET is somehow taking away something from pre-existing player, however a more accurate way of viewing is as an added benefit to new adopters. If you are not a new adopter you aren’t missing out on anything, you have what they are getting and at least half a year of play experience which has an innate value to it as well.