Islam isn't just a title or name of a religion, it's also a word in Arabic which is rich in meaning and has many connections to other fundamental Islamic concepts. Understanding the concept of "Islam," or "submission," is critical to understanding the religion which derives its name from it not only can it make critiques of Islam better informed, but there are in fact good reasons to critique and question Islam on the basis of the concept of submission to an authoritarian god.
Islam, Submission, Surrender to God
The Arabic term 'islam means "submission" and itself comes from the term 'aslama, which means "to surrender, resign oneself." In Islam, the fundamental duty of each Muslim is to submit to Allah (Arabic for "the God") and whatever Allah wants of them. A person who follows Islam is called a Muslim, and this means "one who surrenders to God." It is thus clear that the concept of submission to the will, desires, and commands and God is inextricably linked to Islam as a religion it's an inherent part of the name of the religion, of the religion's followers, and of the basic tenets of Islam.
When a religion originally develops in a cultural context where total submission to absolute rulers and total submission to the head of a family are taken for granted, it's hardly surprising that a religion would reinforce these cultural values and add on top of them the idea of total submission to a god. In modern society where we have learned the importance of equality, universal suffrage, personal autonomy, and democracy, though, such values seem out of place and should be challenged.
Why is it good or appropriate to "submit" to a god? Even if we assume that some god exists, it cannot automatically follow that humans have any sort of moral obligation to completely submit or surrender to the will of this god. It certainly can't be argued that the sheer power of such a god creates such an obligation it might be prudent to submit to a more powerful being, but prudence is not something that can be described as a moral obligation. On the contrary, if humans have to submit or surrender to such a god out of fear of the consequences, it merely reinforces the idea that this god is itself unethical.
We must also remember the fact that since no gods appear before us to deliver instructions, submission to any "god" entails on a practical level submission to this god's self-appointed representatives as well as whatever traditions and regulations they create. Many criticize the totalitarian nature of Islam because it seeks to be an all-encompassing ideology which controls every aspect of life: ethics, manners, laws, etc.
For some atheists, rejection of belief in gods is closely connected with believing that we need to reject all totalitarian rulers as part of the development of human freedom. Mikhail Bakunin, for example, wrote that "the idea of God implies the abdication of human reason and justice; it is the most decisive negation of human liberty, and necessarily ends in the enslavement of mankind, in theory and practice" and that "if God really existed, it would be necessary to abolish Him."
Although the comments above focus on Islam in particular, they should not be percussive as limited solely to Islam. Other religions also teach that the most important value or behavior for believers is to submit to whatever that religion's god wants. Usually this principle is only made explicit by conservative and fundamentalist believers, but while more liberal and moderate believers may downplay the importance of this principle, none go so far as to teach that it's legitimate to disobey or ignore their god.
Islam and Peace
The Arabic word islam is related to the Syriac 'aslem which means "to make peace, surrender" and that in turn appears to be derived from the Semtic stem of *slem which means "to be complete." The Arabic word islam is thus also closely related to the Arabic word for peace, salem. Muslims believe that true peace can only be achieved through true obedience to the will of Allah.
Critics and observers must not forget, though, that "peace" here is inextricably intertwined with "submission" and "surrender" specifically to the will, desires, and commands of Allah, but of course also to those who set themselves up as the transmitters, interpreters, and teachers in Islam. Peace is thus not something achieved through mutual respect, compromise, love, or anything similar. Peace is something that exists as a consequence of and in the context of submission or surrender.
This is not a problem limited solely to Islam. Arabic is a Semitic language and Hebrew, also Semitic, creates the same connections between peace "shalom" and submission in the Bible: "When you draw near to a town to fight against it, offer it terms of peace. If it accepts your terms of peace and surrenders to you, then all the people in it shall serve you at forced labor." (Deuteronomy 20:10-11)
It makes sense that "peace" would involve domination in these contexts because God isn't likely to be willing to negotiate and compromise with enemies but that's what is necessary for there to be a peace based upon mutual respect and equal freedom. The god of the ancient Israelites and of Muslims is an absolutist, totalitarian god with no interest in compromises, negotiations, or dissent. For such a god, the only peace that's needed is a peace achieved through the subjugation of those who oppose him.
Commitment to Islam is supposed to result in a constant struggle to achieve peace, justice and equality. Many atheists would agree with Bakunin's argument, though, that "if God is, he is necessarily the eternal, supreme, absolute master, and, if such a master exists, man is a slave; now, if he is a slave, neither justice, nor equality, nor fraternity, nor prosperity are possible for him." The Muslim conception of god can thus be described as an absolute tyrant, and Islam itself can be described as an ideology designed to teach people to become submissive towards all would-be rulers, from Allah on down.-->