If no person is illegal...

Does this mean that you believe that slaves should legal?

After all, slaves are people.

But the issue isn't the person, but their status. Whether it is a slave or an unlawfully present person.

Yes, the person isn't "illegal", but their presence in the country is not legal. 

The right to enter one’s country, to stay in a country which one has legally entered, and to leave any country including one’s own, have been perceived as basic since the Universal Declaration of Human Rights was adopted in 1948. When individuals claim human rights relating to freedom of movement, they are referring to the same facts and situations that states are concerned with when they assert jurisdiction over their own nationals and over resident aliens. The international law of jurisdiction is the means by which states allocate competence, between themselves, for the prescription and application of authority over events inside and outside their national boundaries.

The only people who have a right to come and go freely into a country are the citizens of that country. It's discretionary otherwise.

And people who haven't complied with the law are not lawfully present in the country.

I don't think it's the best idea to allow people who are not willing to comply with immigration laws to become citizens.

Let's stop playing games with Immigration and get serious about it.