Decentralized exchange requires all parts to be decentralized.

If you exchange BTC to wire transfers, you already lose because banks are centralized and ask questions. LocalBitcoins is somewhat decentralized, it allows trading person-to-person, but it does not work in all jurisdictions and not when you have a big turnover. And it's inherently not safe: you rely on reputation of the trader or opinion of the arbiter.

Cash is decentralized. You can use joint escrow with a trader, swap cash for coins and go home. Both put insurance deposit in 2-of-2 multisig BTC before meeting (must be 200% of the value exchanged from each side). When coming home safe and with valid cash and confirmed coins, both unlock the deposit. This is somewhat secure and better protected from all-observing eye, but: 1) it requires owning considerable amount of BTC from both sides prior to action; 2) it's a physical meetup, so some AML/KYC folks could kick in (especially if they monitor the seller for a few deals already) and arrest all your belongings and maybe charge you with conspiring with some drug money laundering or whatever.

People who want to change their surveillancecoin (usd in banks) or drugcoin (physical paper cash) for Bitcoin must realize these inherent limitations. The best strategy is to not do anything illegal, buy a bunch of coins once on a safe platform or from trusted people you know, and then simply secure and hold your stash until hard times are over and you can simply buy things with it without exchanging back to fiat.