All gods are aspects of the same God
"All gods are aspects of the same god" is a proposition that some more liberal theists use to explain away the Argument from inconsistent revelations. It is commonly stated by Hindu and New Age believers, as well as by apologists who are no longer strongly associated with a particular religious tradition.
One can see that Islam, Hinduism, and Christianity often use similar arguments and psychological tricks, but that none is particularly more convincing than the others. Most believers are either unaware of this problem, or ignore it, or argue that some particular argument works better for them than for other religions. Alternatively, an atheist concludes that they are probably all wrong and disbelieves in all gods until one religion comes forward with more convincing evidence.
However, some liberal theists, particularly those with misguided multiculturalist intentions, often try to take the reverse tactic and believe that every religion is true. Often these same people will claim that criticizing any particular religious tradition (or stating that any particular one is superior) is a form of religious intolerance or bigotry that denigrates others' beliefs.
These people are then in a bind, where they can't accept every religious statement that comes along without being extremely gullible and/or seeming to pick favorites. On the other hand, they can't reject these statements without feeling bad about "denigrating" other people's beliefs. They are consigned to a sort of murky assent, where they claim that somehow, perhaps "mysteriously", all the things that different people believe are true, despite how bizarre many of these claims are.
Blind men and the elephant
The blind men and the elephant is a parable about subjective experience and how peoples' experiences are not necessarily contradictory. It imagines several blind men attempting to describe an elephant without seeing the overall animal. Each man forms a different impression of the elephant, depending on the area that has been experienced. One thinks the elephant is snake like and hangs vertically, another believes it is hairy and rough and yet another believes the elephant is hard and smooth. The contradictory accounts of the elephant causes much confusion between the blind men. In some versions of the story, they begin to collaborate to understand the elephant more fully. 
The intent of the story is that different religious experiences are not necessarily contradictory, since they have only experienced one aspect of God or spirituality. Arguably, there could be a single objective truth but everyone is different and therefore experiences it differently.
The religions themselves are incompatible and intolerant
First off, it should be noted that almost any pair of traditional religions you care to name are on some level incompatible with each other. Hindus may be willing to accept a lot of different gods, for example, but for that very reason Hinduism is incompatible with every major Abrahamic religion. This is true not only in the sense that they tell different stories, but also because their moral commandments and practices are in direct opposition. When Yahweh demands that only he may be worshiped and repeatedly commands his followers to drive out and kill worshipers of other gods, destroying their temples and religious artifacts in the process, that's not a trivial inconsistency.
The truth is, religious intolerance of one form or another is part and parcel of most religions, and to deny this is to be woefully ignorant of basic history. If all these various gods are aspects of one God, He must be crazy, cruel, or both, because His extremely inconsistent revelations and denigration of all His other religions have led to countless wars and lives lost over thousands of years.
You don't speak for all theists
Despite the feel-good message of tolerance and respect in this message, it is also very presumptuous. Walking into the average church, mosque, or (non-polytheistic) temple, and saying something like "All gods are the same God" would probably not get you a whole lot of supporters. You can't just say "you believe in a God that's the same as every other god" to most religious people without being rather rude, because it's intrinsically arrogant to tell other people what they believe.
Anyone who thinks that most religious people really would agree with a line like that needs to get some broader experience, because that's not how the world works right now.
Not all gods are the same
Even though people do believe in some sort of god, some people believe that animals and/or idols are god/s. This goes against the definition of what most religions define god to be.
What about Polytheism?
Polytheism, or the belief of multiple gods, contradict what most religions when they say that there's only one god.
Countering the tale of the Blind men and the Elephant
The tale used above could be seen as possibly misleading, some sort of false analogy, for this reason: what the 3 blind men feel in the story is an Elephant existing in the physical realm, an element that can be easily proven to exist and with relatively understandable characteristics, a being other people with fully functioning eyesight can witness and analyze very clearly: Who are these beings with full knowledge about the elephant and its proprieties supposed to represent, if humans can only be the blind men according to the story? Is is very probable the theist will claim that the non-blind people are the theists of their own religion, but unless they can prove that this is a fact and not just a personal opinion that is just as valid as that of a different theist saying it is his group that see the true nature of a god, it isn't to be taken seriously. One could also compare the reality to this tale instead, where 3 blind men are trying to touch something in the air, one is saying "The X (supernatural element that supposedly exists in the air) is hard and smooth", another says "The X is spiky and cold", and the 3rd "The X is burning hot and fuzzy"; in other words, the 3 of them at times give the unfalsifiable entity mutually exclusive proprieties that completely contradict what the other says. Anyone with a grasp on reality objectively would see that there is something illogical or at least apparently impossible in the while picture. Atheists or Skeptics wouldn't necessarily be the people with good eyes who see the truth in its complete form, they would simply be people who demand some falsifiable proof for this mysterious X everyone speaks of differently, as well as its exact nature.