Humans being what we are, if there is a supply and a demand, a market will form. In gaming, there is clearly a supply of people who have time and want money, and people who have money and want time.
It is all very well to argue in the abstract that this market should not be permitted, but while we play in virtual worlds, we live in the real one -- and as we all know, if a legal market is not available, an illicit one will arise.
In games, this illegal market is RMT. RMT has numerous pernicious side effects for both legitimate players and the developers; legions of botters, ripoffs, significant customer support expenses, etc. One tactic to address this is to create a legal, regulated market -- and thus we get PLEX, CREDD, and now DAC.
Keep in mind that with these tokens, you are trading game time (and thus real-life $) for in-game resources that someone, somewhere had to expend effort to gather or create (as opposed to being created by the developers in a cash shop) - and because it's a legal market, that source is less likely to be a bot. Also note that the market tends to self-regulate due to supply and demand.
Tokens like DAC become P2W when you can use them to buy advantages (and in particular, advantages not organically available in-game) in the developer's cash shop.