[TYPO3-dev] Overriding TCA conf with pageTS - why options restricted?

[Stig Nørgaard Færch]

With page TSconfig you can override some of the TCA field configurations.
For example you could write:
tt_content.columns.title.config.size = 50

But you cannot do this:
tx_cal_event.columns.calendar_id.config.type = passthrough
tx_cal_event.columns.calendar_id.config.default = 4

This would set the type of the field calendar_id to passthrough and then 
set the value to 4. The field will not be shown, but will be set to the 
default value. This is not possible with TCAdefaults.

This is not possible because of a whitelisting of possible keys.

I know that I could just install EXT:tcamanipulate, - but I wondering 
the reason of the whitelisting. Security or.. ?

/Stig