Quite simply I'd like to internalize all externalities so that market forces can determine equilibria. So yes, I think if we could effectively determine provenance, I would like very much to enable that for all things - diseases being the obvious ones, but certainly anything else where externalities exist to some trackable degree (carbon emissions are an obvious one).
My rationale for this case is quite simple. I have very effective protocol around this disease, high risk tolerance, and I want to retain the life I had before (going out, restaurants, clubs, etc.). In exchange, I'm willing to allow you to sue me if I get you sick. I think this will create a freer society, and allow people to find their own position on the risk-benefit curve. It doesn't make sense to subject me to the conditions less-risk-tolerant people want. However, it doesn't make sense for me to subject them non-consensually to conditions I want. A good mechanism to balance these things is a near-continuous universal value measure. A good near-continuous universal value measure is money.
FWIW I've rewritten your question from "why do you feel you are entitled to sue..." to "why do you think it is a good idea for society to permit people to sue..." since I think that's more interesting. The answer to "what gives you the idea that you are entitled to sue" is "nothing, since I do not believe I can right now" which is sort of a boring (though correct) response.
Of course the whole thing is moot. Hard to prove who really caused an infection when community transmission is rampant.