If it is 1 vote 1 witness, you only need 20% of all SP to get 4/20 witnesses and paralyze the network. In this situation you can block all hardforks till you get your way.
That is a good property. If a change is too contentious, it shouldn't occur. Everyone on the network agrees to the current protocol. But we shouldn't force changes that are against the will of a large portion of the network.
Now you need 51% to do this which is at least a majority.
Tron seemed able to control a considerable number of witnesses with just the 20% (STINC stake). Also to need a majority to block a change is ridiculous. That means a change opposed by 49% of the network could be implemented.
Tron with the help of exchanges and proxy.token had 50% of witness voting SP. It doesn't matter if they only actually had 20% of all Steem. This just shows how we don't want to make things any easier to abuse.
Although in theory less than 50% of people should be allowed to block an undesirable change, in reality this will be abused. So it's important to consider the following:
Firstly, let's imagine they block changes just to make unrelated and unreasonable demands before supporting any changes. It happened on Steem when Justin started adding Proxy.tokens' demands for economic changes. Do we want this my way or the highway tactic to be easier?
Secondly, let's imagine they do something like when a needed change is urgent so it cannot be well debated.
Do you really want hostage situations to become easier where an urgently needed change is blocked to blackmail in an unrelated change?
Want to secure the Hive block chain against an immediate threat? Oops it looks like proxy.token wants downvotes removed before this can happen.
Want to introduce the long awaited SMTs? Oh looks like you will have to agree to make love to Jusin, or they will block it.
No thank you.
Human nature means it will definitely be abused. It was already abused. Lets not enable more proxy.token scenarios.