> Far too slow for any real trading.

Maybe if you're a day or mechanical trader. Although, I personally don't know if that's actually true. Have you tried it? Can you share any data or citations?

> Exchanges exist for trading quickly

Agreed

> they must be centralized due to this.

Have you encountered any definite proof of your conclusion?

> Maybe if you're a day or mechanical trader.

Or swing trader or any kind of trader looking to time the market. Trading requires the ability to execute in near real-time. Block chain transactions and worse, fiat transfers between parties, takes far too long for trading to be effective.

> Have you encountered any definite proof of your conclusion?

They must be centralized to obtain the necessary speed because currently block chain transactions are too slow. Proof is unnecessary, logic is more than ample. One can't trade effectively if ones capital is hung up in "transit" between parties. Exchanges exist specifically to provide fast trading. There wouldn't be any exchanges if block chain transactions were fast enough.

Swing trading does not require the ability to place an order in near real time. You need to have done your DD and generally you just place your order the day before you expect your event.

We don't know that blockchain transactions are inherently slow and we haven't verified that no decentralized architectural/algorithmic/structural solutions exist to coordinating trades. In fact, I can think of one or two. So I'm asking you for data, not hypothesis. Do you have any info from your research about trade order execution times on p2p exchanges over time or userbase size? Or is it just your conclusion from anecdote?