The billionaire Koch brothers (Charles and David) own Koch Industries, the second-largest private company in the U.S. They (and their father Fred before them) have been involved with rightwing politics for decades and have been involved in funding or controlling a wide variety of libertarian-oriented groups. The network of groups and people funded by or controlled by the Kochs is referred to as "The Kochtpus".
There are at least two main reasons to strongly oppose most everything connected to the Kochs:
Other Kochtopus groups (such as Americans for Prosperity and Heartland Institute) are involved in promoting or organizing tea parties. Thus, the self-styled patriots in the Teaparty movement are led in part by a network that advocates for loose borders.
Leftwing opponents of the Kochs would be very wise to point out to the teapartiers that they're being led around by loose borders advocates, but that's difficult for those opponents since the Koch immigration policy tends to help the leftwing and the Democratic Party.
Leftwing opponents should also point out to the teapartiers that David Koch joined with George Soros to give the Mexican government linked ACLU millions of dollars. That too is difficult for those opponents; why point out yet another way in which the Kochs help the leftwing?