Yeah, you can use BTC without a mixer, but what is wrong in using BTC with a mixer? Yeah, nothing. You cannot tell people what they should and shouldn't do, if they want privacy and decide to use a privacy solution, i believe they should be allowed to do so. Even if you are correct that 99.9% of bitcoiners don't use mixers, the remaining 0.1% should be free to use it if they want to.
It's not wrong if you care about your privacy and you can have it with controlling your inputs, outputs well. If you want more, you can use Coinjoin for your transactions and mixers are farther than Coinjoin.
I agree that individually it's nothing wrong when you use Coinjoin or Mixers, but you can have problems with centralized exchanges if you send your bitcoin there after a transaction with mixer or Coinjoin. You might have very small risk of issues with government but with centralized exchanges, risk is not small. Especially in recent months, many big centralized exchanges turned to be favorite targets of DOJ and expensive law fees.