Whenever I think of issues like these, concerning who can come into the U.S., I think of the whole land of the free and opportunity bit. We're supposed to be a place where people can make a better life for themselves. However, I do think that there should be a better filter for people coming in than what we have now. I'm not super knowledgeable of all the circumstances around these issues, but this is just my opinion.
People who come into the U.S. illegally sometimes are just looking for a better life, and some have very different intentions. However, keeping all of them out isn't exactly fair to those who come and work hard and have made good choices. I wish there was some sort of system for that, but it's hard to check someone's intentions.
On another note, changes can still be made to Trump's decision. I'm not in favor of Trump or this decision in general, but it can be changed and edited to be a better filter. (example: they changed it so that green-card holders aren't affected by the ban)
By the way I didn't really read a lot of the posts above this so sorry if this has already been said or annoys all of you