Here's the structure of my argument. I take as a premise the assumption that substantive normative claims must fundamentally concern normative reasons (of one kind or another). The core of my argument thus hinges on identifying what categories of practical reasons there are, about which consequentialist theories may then make substantive claims. When we do this, I argue, we find that there is nothing more for global consequentialism to be besides act consequentialism that avoids silly oversights.
Okay, let's begin. There are normative reasons for all sorts of judgment-sensitive states: beliefs, emotions, etc. But core moral theory is concerned with two categories in particular, the right and the good. 'The good' we may understand as a matter of desirability, or fitting reasons for desire. 'The right' concerns reasons for action. Consequentialist moral theories are those that treat the former class of reasons as having logical priority. Our reasons for action derive, in some sense, from considerations of desirability (value). Different consequentialist theories offer different derivations. Act consequentialists claim that our reasons for action derive directly from the value of so acting. Others (e.g. rule or motive consequentialists) suggest a more circuitous route, claiming that reasons for action instead derive from the value of possessing (say) the character traits that would dispose one to perform the action.
Global Consequentialists agree with Act Consequentialists about our reasons for action. (The right act is simply the one that's best.) But then they purport to make further claims, which is where matters become puzzling. As Pettit and Smith define the view:
Global consequentialism identifies the right x, for any x in the category of evaluands -- be the evaluands acts, motives, rules, or whatever -- as the best [available] x, where the best x, in turn, is that which maximises value.
We previously saw that 'the right act' can be understood in terms of reasons for action. But what does it mean to call other evaluands, e.g. character traits, 'right'?
It is important to note that by (say) 'the right character', Pettit and Smith do not mean 'character such that the agent has decisive reason to act so as to bring it about.' The claim is not about reasons for action. It is just a claim about reasons for desire: the 'right' character is the best (most desirable) of those available. (Note that it may be desirable that Bob have some character trait X, without Bob thereby having sufficient reason to act so as to bring about this state of affairs, since the act may have costs -- including opportunity costs -- which render it not the best act available to him at this time.)
But this claim about desirability is not substantive. It's just a stipulation about how to apply the term 'right' to other evaluands. The fundamental normative theory differs not a whit from act consequentialism. Consider: Act consequentialism presupposes a theory of the good (desirability), and makes one new substantive claim: we have most reason to perform the act that would have the most desirable outcome. Global consequentialism agrees with this, and adds a bunch of stipulative claims in addition: e.g. we can call those character traits 'right' that would have the most desirable outcomes. But there's no new substantive claim here.
Anyone can happily assent to a tautology. A fortiori, Act Consequentialists can happily assent to the claim that we have most reason to desire that people have those traits [of those available] which are such that we have most reason to desire that people have them!
For Global Consequentialist claims (e.g. about the rightness of character traits) to be substantive in the way that Act Consequentialist claims about the rightness of actions are, it would have to be the case that we have basic "reasons for character" like we have reasons for action. But we don't. You can't reason your way to having a character trait. At best, you can reason your way to wanting to have a certain character trait, or else to acting so as to bring it about that you have a certain character trait. There are reasons for action and for desire, in relation to character traits, but there are not reasons directly "for" character traits.
Global consequentialists want to be consequentialists about everything. Since consequentialists treat value - desirability - as fundamental, to be a consequentialist about everything would be to treat all other kinds of reasons as deriving from reasons for desire. But the only other kind of reasons (within core moral theory)* are reasons for action. Given this limited domain available for consequentialists to make substantive claims, we find that act consequentialists are already consequentialists about everything. There's really nothing more to be a consequentialist about.
* = Unless one extends the view beyond the domain of core moral theory. One might be a consequentialist about belief, for example, by claiming that our reasons for belief derive from the desirability of holding a belief. But that's an absurd view. (At least, once we take care to distinguish reasons for belief from reasons for acting upon oneself in a way that will causally produce belief.)
Update: more here.