What are generalizations?
We see generalizations fly all the time on both sides of the theist and atheist camps. Many theists like to claim all atheists are immoral and even supposedly rational atheists have made such claims that all Christians are homophobic or that all Muslims are terrorists. These sorts of generalizations are completely detrimental to the arguments at hand and shows either a misunderstanding or misrepresentation of the actual facts at hand. They represent intellectual dishonesty and are very ugly to put on display.
What is worse is that this also causes those of us who pose honest criticism of an ideology to seem as though we too are making a broad generalization. It allows apologists to ignore the difference between criticism of an ideology and criticism of individuals. They are then able to wave away valid criticism and label it a generalization. This is an issue we as atheists need to address and present our case for what it truly is.
Use proper terms. All, some, many.
The big problem a lot of people have is using the proper terms in their arguments. For example, the phrase "all Muslims are terrorists" is a false generalization. However, if we instead say, "some Muslims are terrorists" this is not a generalization but rather an observable fact. In the same respect, saying "all terrorists are Muslims" is a false generalization because there are in fact terrorists who are not Muslims. Again however, if we change that statement to "most terrorists are Muslims" what we have is not a generalization but an observable fact. The majority of terrorists on this planet are in fact Muslims.
Now, some may argue that this is nothing more than semantics. But in this arena semantics are important because the exact word used, be it all, some, many, or even most, sets the context for the statement. It's the same as making a distinction between the phrases, "all birds are ducks" and "some birds are ducks". One of those is false and the other is true. The only difference between them is that single word qualifier at the beginning. So you can see just how important making these distinctions is.
Let's not be hypocrites
Let me ask you a question. Have you ever said, "I hate Nazis"?
Most of us have and it's one of those things most people would agree on. It seems no one really likes Nazis, and for generally good reasons. But there is a problem here. You see, saying "I hate Nazis" is also a generalization. The flat out fact is that there were plenty of good people who were also members of the Nazi party. Their choice to wear the label of Nazi did not inherently make them bad people who are worthy of our hatred. We have to remember that every child involved in the Hitler youth programs were technically Nazis and many of those children likely grew up to be perfectly decent human beings. However, one can say they hate Nazism and this is not a generalization. It isn't a blanket statement that applies to all Nazis as individuals, but rather it is an indictment against the ideology of Nazism.
The reason this distinction is important is that it applies to religion as well. You see, it has become a common practice for apologists to label any criticism of an ideology as a generalization made against the followers of that religion. This is in no way correct and is merely a deflection used by these apologists to draw attention away from valid criticisms. No religion utilizes this tactic more prolifically than Islam and their many apologists such as Reza Aslan. And this should be apparent when we look at just how quick these folks are to call someone a racist or Islamophobic when someone voices criticism of Islam.
People and ideas are not the same
What people like Aslan or any other religious apologist don't want people to understand is this; People are not representative of any given religion. Muslim terrorists are no more representative of Islam than moderate Muslims are. The fact is that Islam only has one representative and it is the Quran. The same goes for Christianity or Judaism or Hinduism or any other religion. The people who follow those religions are not the measure by which we gauge these religions. Instead, if we are going to make a valid assessment of a religion, we must go to the source, which is the doctrine the religion is founded on. If these doctrines offer potential justification for atrocious behavior, then there is a problem with the ideology. It doesn't matter how many people do or don't follow those specific parts because the people are not representative of the religion, the doctrine is the only representative.
The message I want to get across here is that we need to be careful, not only in how we word things, but also in how we think about them. If you make a blanket statement about Muslims or Christians or any other religious adherents you're going to be wrong and you're killing your own argument. If however, you stick to criticism of the doctrine and you base that criticism on actual facts, you'll always have a strong argument.
Always remember that every person is an individual and because of this blanket statements simply won't work. So keep the word all out of your arguments and criticize the ideology rather than its adherents.