It is important to maintain and enforce the principle of the rule of law, and a fence does that.  Illegal immigrants are openly flaunting the law, and permitting them to enter the country in this way demeans the hard-working individuals who immigrated legally. If people become angrier about illegal immigrants because more of them are coming in without a fence, this may also lead to the negative outcome of poorer treatment of Latinos who live and work legally in the United States. If there were no or very few illegal immigrants, there would be much less tension in communities since everyone would know that all the inhabitants had come there legally.