That's part of the freedom that bitcoin gives you. If a merchant wants to use a centralized exchange for reasons that make sense to him, it's his right to do so. I can tell him about better options, but he doesn't have to listen to me as long as that exchange satisfies the needs he has. If I use the services of such a merchant who then sends those coins to a centralized exchange where they get confiscated for being associated with mixers/underground markets/gambling/whatever, I can't tell the merchant that I am a privacy-oriented individual and he needs to be one as well by not using such exchanges. He'll want his money because the coins I sent him, aren't worth anything to him. Therefore, if this practice of removing value from certain coins that centralized entities don't like continues, it will be the privacy-focused users who suffer the consequences.