In the MCAS case the 'optional' component was an AoA display available to the pilots. Due to a misunderstanding about the design intent, planes without this option also did not display an AOA DISAGREE alert if the sensors disagreed. (I agree that such a simple situational awareness aid based on data the plane already has being a paid option is pretty absurd)

However all MAXes did/do have two AoA sensors, and prior to the fixes, regardless of the AoA display option, MCAS only considered one of them.

In the MCAS, the ‘AoA disagree’ sign allowed more freight to be carried. The pricing segmentation is based on freight, the intent was not segmentation over security levels.

Even if it leaded to lowering security so much that 4 planes crashed in just a few months.

The AOA DISAGREE was never intended to be optional, that was a bug due to miscommunication between Boeing and the avionics manufacturer, if the congressional report is to be believed.

Only the persistent numeric AoA indicator was optional. And none of this had anything to do with freight, there's no difference in capabilities between the aircraft, it's purely about pilot situational awareness.

https://boeing.mediaroom.com/news-releases-statements?item=1...