And trust me, being a tank/healer will get you raid geared for DPS much, much faster than waiting in queue. That, or you'll have to kiss major ass to hope to get a queue buddy. Hardly a "compelling design." You seem to think that being a DPS means you only ever DPS in LFD, and being a tank means you must be the main tank of your guild - no sense.
2) You're contradicting yourself. First argument is that nobody will use tank specs because "they aren't needed in raid" - but if they really aren't needed if you're not a MS tank, then why are we suddenly being "forced" to use tank specs?
As put, plenty of people are playing the DPS specs of a class with tank/healing capabilities and are doing fine. Plenty of priests are playing holy/discipline and are doing fine. Plenty of people just play tanks without off-specs and are doing fine. I can hear out some arguments about why adding in extra specs will make the class work, but only hearing "People will hate being 'made to tank'" is pretty ridiculous, considering the biggest likelihood is that they won't be made to do so at all.
P.S. The majority of people I know who do in fact prefer pure DPS classes simply like to DPS and do not care for tanking or healing. They are not, however, afraid of being asked to tank or heal because their guild knows that they just prefer to DPS (amazing, they actually communicate what roles they like to play with their guild).
In this case, what would said people be losing if a spec is simply added without taking anything away?