Defi is not a scam, just that those who are not try it before look at it as a scam. it's not good to hold your coins long in Defi, because the price can drop at anytime.
Its just a termed for the new hype decentralized finance. What is scam are those projects that made defi hype really look like a scam. There are too many pulled rugs happened in the past few weeks and we can see the effect on it on the long run. Crypto space is now swarming with yield farming types of project. From one to another, major projects started to copied its format like what Justin Sun doing right now. Defi token sun.