In my redraft league, we follow the start or don’t start policy, its the choice of the owner. To me, if not starting a defense, to avoid negative points allows for a team to win, then its a great idea. The goal is to win, I want everyone in my league try and win so its always competitive. Sometimes, there is a great waiver/FAB/FA pickup after the Thursday game and the only player you’re willing to drop is your kicker. So some guys will drop the kicker, not play a kicker, so they can get the FA. Its all strategy; and sometimes, the sitting of a defense or kicker is good strategy.
Dynasty is much more complicated because you have some teams taking for a better rookie draft spot. The way we have it is that you must start every position player slot where you have an available guy to start. For example, if you have a QB not on a bye, you must start a QB. But, if you have a kicker not on bye, you do not have to start a kicker. This mitigates some of the tanking but allows people to have opportunity for strategy.