Here is my problem.
D&D has roughly (if you ignore similar concepts and redundancies) 50 some classes in it. Some are obscure as all Baator (hello factotum) and others feel like natural additions (I'm honestly shocked we made it through 1e without some demon-powered magic caster, because warlock seems right at home).
The question this always boils down to is what should make a class worth being a full-bodied class, and what better fits a supplementary role (either as a later addition in a supplement, a background, a specialty, or whatever prestige idea they add later).
Since there is no objective way of measuring such things, we all default to our "gut" and make value judgments based on our experiences and beliefs. The problem with that is that we bring our own prejudices into the mix. For example, I think the Spellthief from 3.5 is hella-weak in both concept and execution. I could really care less if it was ever made a class again. Others will disagree with me. That's fine. Here's where it gets rough.
I'm of the opinion that the PHB 1 classes (Assassin through Warlord) get a free pass. Why? Because they are iconic to at least one edition of D&D, and if this is the edition of healing, unity, and kumbaya, it needs all the parts from all the editions there. It doesn't matter if your PC is a half-orc assassin or a dragonborn warlord, those options should be out the gate for you in Next. (If you picked a more obscure race/class from a supplement, that might be another story).
Further, I think most people refuse to believe that themes/specialties are fairly lackluster. They're a tree of linked feats, which could be taken separately or ignored completely if so chosen. You can't say X is a specialty without inherently saying "X is nothing but a few feats and should be ignorable". I'd hate to see my 1e inspired DM have to choose between having an OS no feats/specialties in his game and having an "assassin" character available.
Specialties might work for a class that is decisively one-trick (the aforementioned spell-thief might work as an add-on for Sneak Attack) but iconic classes have no business as specialties.
Third, there is a nasty habit to refight the class-wars of the past yet again. Barbarian isn't a class, its a culture. Assassin is a job anyone can do. Monks are too asian, paladins should serve gods, etc etc etc. I think it does us no good to refight these wars. Barbarian has been a class for Four editions now. There has never been a generic, non-asian flavored martial artist in any edition now. We need to get over the fact that these classes have been classes now for a while, some of them multiple editions. They have fluff and crunch differences from other classes. Trying to cram barbarian back into Fighter or Druid back into Cleric is like trying to put the smoke back in the bottle. They've won the right to be classes again.
Now, what does that mean for the rest of them? Well, some of them I think will make it back to classdom but not out the gate (Psionics is
[URL=http://www.enworld.org/forum/usertag.php?do=list&action=hash&hash=1]#1 [/URL] example; its too hard to fit spells and powers in one PHB). Others were grid-fillers that no longer have a niche (an invoker didn't have much beyond "divine controller" to set it apart from cleric, I see no need to keep it around. While I can see a place for shaman as different than a druid). We can debate if we need a dedicated gish class, or if avenger is strong enough to stand alone in some supplement. But I think it really is counterproductive to argue about the PHB. It needs those classes to be successful and they have earned their place.
So lets quit over arguing the validity of an assassin class and start discussing how it should be done, because screaming that it doesn't belong is counterproductive at this point.
