The asset value underlying an ETF can be negative, but then the owner of the ETF will just have a worthless piece of paper. The ETF managers will have a problem on their hands regarding the negative amount, though.
In contrast, a futures contract is an agreement to make a future trade, so it can keep going against you past 0. If you are able to take physical delivery, your worst-case scenario is that you pay the money you said you would, and you get your oil. But if you are a casual day-trader type, you probably don't have the ability to take physical, so you may be in trouble (over a barrel, literally).
I agree with you about the dangers of ETFs and about knowledgeability. I didn't mean to advocate for ETFs on an absolute basis, just to make a relative statement about them vs. futures.