Some no mark fake volume exchange could be doing anything with what you send them.
Absolutely, but I'd suggest that Coinbase selling data to third parties doesn't exactly fill me with confidence either. Just like the two-bit exchanges, we have no idea what these third parties did with the data they obtained or how well the secured it.
but there is also a negative of using it because not all of decentralized exchange are legit and many of them have hacked before.
The vast majority of "decentralized" exchanges which were hacked were not actually decentralized at all, but simply used the term as a flashy advertising slogan. The whole point of a decentralized exchange is that you keep control of your own coins and there is no central server or wallet which can be hacked.
but I guess that's better than using an unsecured decentralized exchange and risk your funds of possibly lossing everything.
I'm curious why people keep repeating this. My guess would be you have never actually used a proper decentralized exchange and understand how it works. You don't deposit your coins to the exchange, and so the risk of loss from your account being compromised or the exchange being hacked is significantly lower than with a centralized exchange.