Most liberals I know think they shouldn't but that its stupid to police this aspect of people's behavior if they are on EBT. Most liberals might even feel more comfortable regulating everyone's behavior by taxing unhealthy foods than they would just bothering poor people with it.
Chips ... I think you should probably allow parents to spend EBT to buy a bag of chips for a hungry/picky kid in a pinch.
As someone who lives in a neighborhood where most tapwater is still delivered by lead service lines, I'm sympathetic to the argument that it provides hydration. I'd prefer that my tax dollars went to solving that problem more directly, however.
It feels much more like spite politics: We can tell these people whose morals are so bad that they need our money to survive that they cannot spend it on what we think of as junk food. That is a luxury only us hard working folk are permitted. When you are poor, you cannot suffer alone, you need to know that we are making sure you feel extra pain. Please be motivated to be better.