What tactic is used when someone states "You must not care about this issue at all since you disagree?"

The tactic involved in the statement "You must not care about this issue at all since you disagree" is categorized as an Ad Hominem attack. This approach focuses on undermining the individual rather than engaging with the merits of their argument. By suggesting that a person's disagreement indicates a lack of care or concern about the issue, the speaker diverts attention from the actual points of contention. This type of reasoning implies that the individual's character or motivations are relevant to the argument, when they may not be.

Using Ad Hominem attacks can be particularly misleading as it seeks to dismiss a viewpoint based on the perceived character of the person offering it, rather than addressing the logic or evidence of their claims. This strategy often results in a failure to engage with the real issues at hand, leading to unproductive discussions. Hence, it is important to be aware of such tactics as they detract from rational debate.