The phrase "belief in X" is critically ambiguous, and this ambiguity often works against the interests of the atheist/antitheist side, as it affords the religious another escape hatch for avoiding seriously facing criticism.
If I say "I believe in Bigfoot", what do I mean? I might mean one or some of three distinct things. First, that I believe, or take myself to believe, that Bigfoot exists. This is a propositional belief, if provable, a mere thought otherwise.
Second, that I commit myself to Bigfoot. The term "belief" can be used to express a sort of overall life path or life orientation, and thus an adoption of a set of unquestioned/unquestionable grounding assumptions which act as the basis for all subsequent beliefs and attitudes. Strictly, these grounding assumptions are not beliefs since they are the standard by which everything else is judged they are thus, by definition, unable to admit of proof or disproof. They can be replaced (or, more accurately, uprooted) but never shown false.
Third, that I trust Bigfoot, and consider his views or attitudes worth taking seriously, as sincere expressions of a trusted friend or worthy foe. This is "belief" as "believe in", taking someone as important.
Call the first "existential belief", the second "commitment belief", and the third "belief as trust". Atheists don't tend to get that theists could mean any one or some of these. Theists don't tend to get that all are untenable; retreating from one to another only delays this realization.
Existential belief is easiest (for me) to undermine, as it is a straightforward belief in what cannot be proven, and is thus only a thought. See previous post on belief (here) and also on rational faith (here). It won't work to ground theism.
Belief as trust is next easiest to undermine, as it depends on the first. If there is no actual god -- if the belief that there is a god is either false or impossible -- then any expression of trust towards god is empty. You may as well trust in Bigfoot -- or fairies. If, by contrast, the attitude of trust is not empty or towards some null object, it must be towards something that is masquerading as god. Some obvious possibilities include a parent, a trusted advisor (such as a priest, many of whom are morally decent people), one's internalized view of social mores, or one's own views externalized as the opinions of someone else. Regardless of the legitimacy of trusting nay of these sources, I think one should first acknowledge the real thing that one trusts, rather than cloaking it in the guise of god.
Commitment belief is the most difficult to show untenable. It's not enough to point out the practical consequences of this or that set of commitments. After all, while there are theists who are tortured by their commitments and would be better off without them, there are equally well miserable atheists who would be happier if they could believe, and happy theists who would be lost without a grounding commitment to the divine.
Similarly, it is not enough to point to theoretical inconsistencies within a set of grounding commitments, as when the Roman Catholic tries to become an evolutionary biologist. Accommodation between propositions is always possible, as a matter of logic, as long as one is sufficiently willing to make the necessary exceptions and excuses. Human cognition is also curiously resilient when it comes to accepting tension within the set of commitments, never mind the set of beliefs built on top, so it is always possible for theoretical inconsistencies to be met with a simple shrug and a smile.
To my eye, the best approach is to mount a moral argument, originating (likely accidentally) in Milton, and repeated by others, such as Christopher Hitchens. (Aside: I liked Hitchens' prose and his willingness to put himself on the line for what he believed. See, for example, the video -- it should still be online -- where he submits to being waterboarded, something no other support of the Iraq war could bring him or herself to do. Many of his opinions were odious, though, and his arguments tended to be poor. In that, he shares more with Richard Dawkins and Sam Harris than I think any of them realized.) Committing oneself to God makes one a slave; and slavery is morally degrading, and thus intolerable.
Here's Milton, writing as Satan (hence, I think he didn't mean us to accept the view):
... Here at leastIt has been echoed again and again, by atheists like Hitchens, Satanists like LaVey, and Christians like John Stuart Mill, that no human being (in full command of his or her faculties) should tolerate being compelled to submit to another. Given that it is wrong to be compelled to submit to another human, it should be worse to be compelled to submit to a higher being, like a deity.
We shall be free; th' Almighty hath not built
Here for his envy, will not drive us hence:
Here we may reign secure, and in my choyce
To reign is worth ambition though in Hell:
Better to reign in Hell, then serve in Heav'n.
Anyone who disagrees with this point is, of course, defending slavery. And good luck with that.
If commitment to god can be shown to imply slavery, then it is wrong -- morally -- and should be uprooted and replaced.
One obvious objection to deal with at first is that one chooses to submit to god, and there is therefore no compulsion. Any religion that takes seriously the notion of hell, heaven, or even karma (derived from commitment to the deity or the faith) cannot advance this point, any more than a mugger could argue his victim gave over his wallet voluntarily -- after all, he could have just chosen to be shot. Being deprived of ultimate reward is also a punishment, albeit a more minor one. The mugger point still applies: even if he swears to return the money with 1000% interest in 10 years, he still forced his victim to give over his wallet. Finally, for those few believers whose religion neither punishes non-believers nor rewards believers, one has to wonder: what difference is there between commitment and non-commitment? If there are not eternal or divine consequences, aren't we once again cloaking something else -- commitment to social stability, or to a moral value, or to a rational purpose -- in the guise of god?
So: does commitment to god imply slavery or not? Any god that demands obedience is clearly a slaving god. Any god who rewards and punishes is a slaving god, as argued. And any other god doesn't really seem like god any more. So, commitment belief is untenable, too, as it places the thus committed person in the position of a slave.