I think you may have missed the point of the article. I don't think it's reasonable to assume democrats don't want to do anything about immigration. Trump and Biden both have basically the same plan to address illegal immigration. Harris' plan is similar to both of theirs as well.
Illegal immigration is not nearly as serious as the average Republican might believe. They add strain to systems already working beyond their limits, but legal or illegal migrant workers aren't displacing citizens at work and aren't leading to the kinds of outcomes Mr. Trump would like his followers to believe. It does happen occasionally, but not enough to justify the alarming hate filled rhetoric.
The problem is that "poisoning the blood" is nakedly racist. The phrase has been used for over 100 years as a dog whistle for white nationalism. How can you have a rational discussion about addressing the real problems that enable illegal immigrants (American businesses hiring them) or the additional strain they put on already over worked and under funded public services if one side is ideologically set on the notion that migrants are evil?
I don't think it's reasonable to believe that democrats don't want to address the border. Safe, legal migration into the United States benefits everyone. If we streamlined the legal immigration process and cracked down hard on businesses and individuals hiring undocumented migrants, that would address the bulk of migrants illegally crossing our borders.
Perhaps we make it a felony with mandatory jail time (per infraction) to hire an undocumented worker or own a company that employs them. Or perhaps we remove the exemptions some types of businesses enjoy from paying minimum wage. One of the reasons businesses hire illegal immigrants in the first place is they are cheaper than American workers because you can pay them less than minimum wage.
Right now there are a lot of businesses that benefit from cheap migrant labor, if we can break that trend, some of those businesses will fold, for sure. But do we want to let failed businesses that can't stay open without breaking the laws of the United States to continue to operate?
I think a better title for this question might be "What issue do you feel strongly about but have weak arguments for and can only tolerate agreement with your position about?"