I'll bite. I think there is a difference between "should they" and "should they be able to."
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.
If we want healthy food we have to regulate the food-makers. Everything else is skirting the edges of the problem. Taxes, EBT restrictions, none of that will make a dent.
Taxes like that seem all but required if you want to have a chance at a functioning single payer system. 0 chance single-payer will works with so much freedom to destroy yourself then make everyone pay for it.
EBT is already money with strings attached - you can only spend it on food. I don't see narrowing the definition of "food" here to exclude soda to be a huge problem.