Do you support open borders (why/why not)?

Let’s just put this question out here. This is purely hypothetical. I am not saying that Biden is going to open the borders. I was inspired by what someone said in another thread: should traveling between the U.S. and Mexico be as easy as traveling between California and Nevada? Why or why not?

Please no one-word “yes” or “no” answers. I’m interested in the reasons behind the answers.