A whale cannot prevent any STEEMPOWER holder from accessing their RC's. Nor can a whale take STEEM from you that you have purchased.
I clearly state that for a USER it's only necessary right now to own the STEEMPOWER that you need to transact with the network. And in the future, you won't even need any STEEMPOWER if the application/community has an RC pool.
Big stakeholders can indeed downvote posts they don't like to zero in STEEM but unless whales want to become a whale in every SMT that will be created they won't be able to do so for every community/applications build on STEEM in the future.
It doesn't mean STEEM can't go to 5 cents, but not for the reasons you mention because they are not valid.
Well, learnelectronics actually does have point. Where do the rewards come from? Inflation. Why do people dislike inflation? It erodes the value of the money in their bank account. When someone with more stake than someone with less stake downvotes something that has been upvoted, the upvotes become negated. This hurts both the author and the curators. And exposes them to harm via inflation.