Witnesses already have the power to censor like this.
Yes I understand the technical side of it. However, the political side of is far more complex.
You are introducing a rule that says that certain forms of censorship are okay. That is a very gray area and can easily be subject to great political conflicts and sliding interpretation.
However, as long as some honest witnesses remain, voting out the misbehaving ones is a straightforward matter.
The issue I'm raising specifically with regard to the property rights of all SP holders and their access to a fair share of bandwidth (which arguably provides the foundation for the entire value of STEEM) is that: a) large holders can have different interests from small holders, and b) what is "misbehaving" becomes vague and subject to a morass of political reinterpretation and influence games under this proposed system.
If large holders, and the witnesses they elect, decide for example that only people with more than 100 MV are allowed to make more than two transfers per week then small holders have no recourse. Or that only people with more than 100 MV can transact without fees. Etc. This can obviously be done in less blatant ways by witnesses and their large stakeholder supporters making smaller and more subtle changes over time with little scrutiny.
The simple and clear rule that blocking transactions that conform to the protocol rules is censorship and always considered unacceptable (except possibly pragmatically for a short time as a temporary bug fix pending a hard fork) is a clear line that possibly can be maintained as a core value by the community and stakeholders. I'm far less comfortable with a rule that says that blocking valid transactions according to witness discretion is okay under some circumstances but not others, especially when it implicates the core value proposition and property rights of SP holders.