Yes, they're negative rights.
However, I'm not sure I agree that property rights can't be violated or that we don't have some moral obligations.
Let's say that someone who is starving comes upon your cabin in the woods. Would it be morally impermissible for them to break in and eat your food? Perhaps you think it is, but then what else should they do, die?
What if a child was drowning and you were physically able to save it, could you just walk by? It seems that you do have an obligation to save the child. Similarly if you couldn't but someone close to you was walking by who could, would it be morally impermissible for you to force them to save the child? How about if it was to save a sinking boat, full of children?
What if everything in a small island was owned by a few people, who collectively worked on their land and homesteaded it. As a result, there are a few remaining others who lack access to basic food and water. Would it be right for them not to share their resources?
Perhaps you think these examples should lead us to justify a welfare state, but I disagree. 1) These examples are about people dying, yet in developed countries, the absolute poverty rate is virtually zero. Welfare is for people who are already alive and who have access to some means of resources.
2) These thought experiments are also all one-time interventions. Alleviating poverty is an ongoing system of coercion. Similarly, we can only alleviate it, and not necessarily fully eradicate it.
3) In real life, you may be uncertain whether forcing something to save a drowning child will actually save them. The guy you're forcing might also knock some children into the pond, who will then drown. Given the difficulty assessing these probabilities, you would need a significant reason to think forcing someone to provide assistance would be helpful.
If the intuitionism I sketched out is correct, this is a powerful argument. Using people's common sense ideas of what justifies a welfare state, we can show that it is unjust. Of course, all welfare states come down to political authority, and so we'll also need to use our intuitions to sketch out arguments against those, which I think we can.