They are claiming that the unvaxxed are using a greater share of our finite healthcare resources. It is questionable whether or not this is even true - recent data points to the vaccines doing almost nothing to protect anyone - but even if the argument were valid, you won't see leftists applying it to any other choices people make. No one is denying healthcare to fatasses or drug addicts or criminals or illegal aliens, yet all of these people have made selfish decisions that strain our healthcare resources. The left simply doesn't care about coherence or consistency of principles or values. Leftists will say whatever they need to say to get what they want in any given situation.