I tried to make this concise, but I couldn't. I organized it into three main points, at least. Please let me know if you want me to clarify anything or if you want additional resources.
Since September 11, there have been 36 individuals that have perpetrated Islamic terrorist attacks in the United States.
According to The State Department, The UNHCR, and the Center for Immigration Studies, over 16.7 million immigrants and refugees have entered the U.S. since 2001.
This suggests that .000216% of all immigrants and refugees (assuming the aforementioned 18 individuals were immigrants or refugees [some of them were naturally born US citizens]) have perpetrated acts of Islamic terror since 2001.
Point A: The system is not failing, as it admits enemies of the state at almost a 0% rate (.000216%).
Continuing Point A, I have worked closely, and had in-depth conversations with Refugees from Iraq and Syria, among other countries, who are Muslim. The 20-step vetting process (which involves security and background checks by four Federal Agencies, as well as the United Nations, and lasts two years) to admit this demographic is already arguably the most extensive vetting process undertaken by any country in the world. Hearing the stories of the levels that they have to go through to reach asylum in the US has made the depth and the degree of the refugee screening process a reality for me.
Point A.1: Extreme Vetting is already the reality.
I shouldn't have to continue beyond points A, but assuming that the system does need to be overhauled, the executive order stipulates that no immigrant visas will be issued from the 7 identified (Muslim-majority) states and that no refugees will be admitted during the three month period. It also claims that when resumed, the US Refugee Admission Program will "prioritize (victims of) religious-based persecution, provided that the religion of the individual is a minority religion in the individual's country of nationality." This is a clever way of saying that Christians will take priority over Muslims. We know that he advocates for anti-Muslim immigration and refugee admission policies because Trump called for a Muslim immigration ban during his campaign.
Here's the problem with that: this amplifies the target that militant Jihadiism has already placed on the United States. I know from my time in the intelligence community that Jihadi terror groups' primary recruiting tactic is to make Muslims feel like their home country doesn't want them. When a Muslim feels disenfranchised and isolated in their home country, the Islamic State welcomes them in with open arms, and thus new Muslims are radicalized. We know this because we have expansive Jihadi publications (which I have seen and read in Arabic) that outline Jihadi recruiting tactics and isolation as the first step in radicalization. I can provide a long list of resources if you are interested in the sources of this information. This executive order plays directly into their game plan.
Point B: This Executive Order will invariably increase Jihadi recruitment and anti-American sentiment and action around the world.
Continuing, the argument that this is a temporary measure is one that I hear often. My primary issue with this argument (besides my contention that even a temporary rejection of an entire race of people is still un-Constitutional, un-American, and un-Christian) is the precedent it sets. If the United States accepts this method of closing our doors to people who are different than us as a means of "protecting ourselves," then the next time that it is proposed, there will be a justification for more extreme measures. This will be something that neo-conservatives can build off of, and the potential for it to become a precedent that initiates much deeper and darker atrocities against Muslims (or any one else that those groups choose to target) is too dangerous to be complacent about. Many incidents of genocide in recent history have begun with a smaller, more "acceptable" measure that went unchecked.
Point C: Temporary rejection of basic Human Rights (see Universal Declaration of Human Rights, Article 14; 1951 Convention regarding the Status of Refugees, Article 3; Convention against Torture, Article 3; et al.) is still a rejection of Human Rights and can be referenced to justify greater future atrocities.
Conclusion: This EO is about playing into irrational fears of brown people. While that is my subjective conclusion, we can analyze the facts and the data above and understand that the harm that this will cause to our country, our image, and our morality as a nation are not worth the results that it might possibly achieve.
Moreover, I spoke with Rema, my Syrian student, today. Her eyes went to the floor as she told me that her Sister and brother-in-law are in Turkey, trying to join her family here in the U.S. This is the impact, real people being told that they aren't wanted, that the country in which they have placed their hope (because that country promised to welcome them in) has essentially said, "we don't want you." As anecdotal as that may be, it's why I've shed countless tears over this EO and over the country's response. Please, please, please have compassion on the victims of this. Look at the facts, not what you see in the media, not what you feel, not what your friends feel. You don't have to hate Trump to disagree with this decision that he has made. Please, please, please disagree with it.