the first part of your statement is implicitly false. If it is true, it has to be false, because if "anarchists don't actually agree on anything", then there has to be anarchists who disagree with this statement. What's more if we venture away from U75 anarchists to my website
www.ResistanceMP3.org.uk, you will find anarchists who have no problem discussing anarchism. Lastly, in your very acknowledgement that U75 anarchists act collectively, "collectively, behave like clams. [.......] as soon as the conversation turns to the U75 anarchists views, like clams their mouths snap shut.", you demonstrate that even the U75 anarchists have enough common ground, to act spontaneously collectively.
However that is by the by, because this statement "just shows that you haven't thought it through for yourself. Only people in cults agree with each other." IS commonISH to virtually all the writings U75 anarchists, and most I have come across outside. It's this kind of Christian individualism attitude, that people can only come as individuals, by their own effort, on their own, to an anarchism,,,,, which needs some explaining. It seems to have no evidential or logical basis, yet it is so prevalent you must have some explanation.