Generally speaking, the door zone is not something that is widely understood and many some road users are not sympathetic to cyclists who avoid it.
There are many different scenarios that potentially put you into conflict with car doors and other road users. Pulling out to pass a single, stationary car with 5ft of clearance is unlikely to engender too much hostility from following traffic, pretty much regardless of your speed (although last sec swerves are inadvisable). Cycling 4-5ft out along a road with on-street parking on both sides (with two way traffic but no central lane marking) for 300m at 12-13mph will be far more likely to garner beeps, shouts, tailgating etc. If you understandably feel intimidated, you might want to indicate, check the parked vehicles as best you can for occupants/signs of movement and stop next to a parked car. In the same situation, if a car heads towards you, you will need to enter the door zone to stop or slow dramatically, if there is not a convenient gap to pull into. Filtering through traffic that has come to a standstill might put you in the door zone if traffic is dense in both directions – in such situations you need to be moving very slowly in order avoid or mitigate the consequences of a car door being opened in front of you, or just hang back depending on the length of the queue. Same direction lane splitting gives you twice the opportunity to get hit by a car door etc etc etc