The negative slope is not just because people think there is going to be a crash, it is also just function of supply and demand on options:
- Many investors want to buy protection on their portfolio, and there is no natural seller so it's the speculator who end up taking that side of the bet, but obviously only if there is a sufficient premium
- with low interest rate, people have less money to spend when they do capital guaranteed structures, so whenever they buy puts they will usually also sell calls to cheapen the total option price. This again will create extra supply
Besides, the thing about lack of automated trading in some emerging markets might be true, but that might not necessarily mean reduced crash risk.
One of the reasons that the vol of an index goes up when the index goes down is that people just trade all the constituents without much discrimination, which pushes the correlation up, hence the vol of the index. That might actually be worse when performed manually by humans than when done by machines which could potentially correct for imbalances between shares (i.e. sell bad ones and refrain from selling good ones).