Though an official ruling of Taboo is that you cannot partially follow Taboo, per an investigator :
Investigators are not forced to adhere to the restrictions on this list, but if an investigator chooses to do so, they must do so in full (an investigator cannot pick and choose which restrictions to use).
The reasoning behind this card getting +3 Chained is that :
We’ve also taken the opportunity to chain everyone’s favorite Eschatologist, David Renfield (+3 experience); the reasoning behind this change is in anticipation of many of the new cards coming in The Scarlet Keys Investigator Expansion, which are likely to propel this already popular powerful card to new levels of power.
So I think it is quite fair if a player is selectively following Taboo for something like Dr. Milan Christopher, but not David Renfield if you don't have any Scarlet Keys cards in your deck, if you are just looking to play with doom the old school way. (Perhaps for Daisy Walker deck that could include both.)