You should hit them back. But it can't be a free shot, without being bountied, because this can be abused in PvP wars where only incoming hits can be bountied but not outgoing. But my advice to you, vetlet, is to hit back or bounty, but not both. A PvP'er won't bounty you for a returning slap, because that would go against their own principles.
Useful to know: I wouldn't go with both as that is just cheeky. But see your point about PvP wars. Ah well.
(PS: please note a leveller NOT complaining about the change!)