Off-hand here are three pragmatic costs of doing so, as stripped of moral language as I can get them:
1) Cognitive dissonance. For most of us, behavior influences belief, so behaving as though the presented evidence wasn’t compelling can (and likely will) interfere with our ability to properly incorporate that evidence in our thinking.
2a) Reputation. If I fail to signal internal state reliably, I may develop a reputation as an unreliable signaler. There are social costs to that, as well as nastier words for it.
2b) Reputation, again. Evidence of true things is a valuable thing to have. If someone gives it to me and I refuse to acknowledge it, I’m refusing to acknowledge a gift. There are social costs to that as well.
3) Operant conditioning opportunity costs. Making an argument that others find compelling is emotionally rewarding for most people. If the person you’re arguing with is one of those people, and you signal that you found their argument compelling, basic conditioning principles make it more likely that the next time they have evidence you ought to find compelling they’ll share it with you. Conversely, if you don’t signal it, they’re less likely to do it again. Therefore, continuing to argue as though the evidence were uncompelling means losing chances to get benefits later.
Off-hand here are three pragmatic costs of doing so, as stripped of moral language as I can get them:
1) Cognitive dissonance. For most of us, behavior influences belief, so behaving as though the presented evidence wasn’t compelling can (and likely will) interfere with our ability to properly incorporate that evidence in our thinking.
2a) Reputation. If I fail to signal internal state reliably, I may develop a reputation as an unreliable signaler. There are social costs to that, as well as nastier words for it.
2b) Reputation, again. Evidence of true things is a valuable thing to have. If someone gives it to me and I refuse to acknowledge it, I’m refusing to acknowledge a gift. There are social costs to that as well.
3) Operant conditioning opportunity costs. Making an argument that others find compelling is emotionally rewarding for most people. If the person you’re arguing with is one of those people, and you signal that you found their argument compelling, basic conditioning principles make it more likely that the next time they have evidence you ought to find compelling they’ll share it with you. Conversely, if you don’t signal it, they’re less likely to do it again. Therefore, continuing to argue as though the evidence were uncompelling means losing chances to get benefits later.