They appeal to people who can’t actually think. It’s a simple question really, do you want open borders or a secure border? If you want open borders (and many of the new generation of Democrats do) then what’s the point having immigration at airports or any security on borders?
Before the existing walls were built and other security measures added, there were 1 million apprehended crossing illegally per year across the southern border. That number is now down to less than half a million (still a crazy number, and that’s just the ones caught). In 2017, 17,000 were apprehended who had prior convictions in the US. The Democrats would happily let all these people waltz in.
The US has the most generous immigration policies in the world, 1M legal new immigrants per year, along with another 50-100K asylum seekers. The great majority of immigrants are from Hispanic and Asian countries, so it’s hardly a racist policy.