livedarklions no apology needed, I didn't sense any negativity on your part regarding sidewalks and bicycles.
IMHO there are times and places where that may be the least-risk option in a particular rider's mind, and if we've not been in those exact situations it is unfair to cast aspersions (again, IMHO). They're also a mixed bag with their own inherent risks and challenges, such as driveway cross-traffic not looking for anyone faster than a walker as
himespau illustrates. (these and subdivision entrances are a danger zone, particularly when going against traffic, since drivers seldom look "downstream" before rolling / turning to the right).