FUD.  The system won't fail.  

What they are cautioning is that if hype is too great, usage of the network to execute a smart contract may not be economical.  In that sense, the economical model will "fail".  This happens all the time in markets around the world everyday.  People handling their purchase as an investment means they speculated others would be willing to pay more to use it (get it from them).  However, if the execution of contracts are too expensive for X application, the developer will not be able to afford it.  And will not use.  If enough devs do not build contracts to utilize this new system speculator will realize they overpaid, so they decide to lower their sale price.  Enough sellers "giving in" to the buyer's ask price evokes an emotive response and people panic.  That same developer looking to use the network looks at it again and says woah, it will probably cost $800/year to run my app on it. So he buys 5 years worth of "coins" because it is now cheap.  In this case, developer got a deal they found fair and speculator helped sustain early development.  Or maybe dev who wanted to use it thought original asking price was fair and speculator made a good bet.  That's why it is called speculating and not investing, you are trying to value something very difficult to quantify and trusting a group of people to achieve a goal.

The warning in the terms of service is akin to the warning on bleach and other cleaning products cautioning you not to ingest.  It's obvious to those that understand the product.  And for those that do not understand the product, they are offering full disclosure which I would consider the complete opposite of a scam.