When I am using a light for defensive purposes, the last thing I want is the light giving the bad guy more information than it gives me. That is the risk one runs when using a light in constant on mode, or possibly even unintentionally clicking it on. I want to quickly illuminate an area, deactivate the light quickly, and then move to the next area. Leaving the light on for more time only risks drawing fire. In an unusual circumstance where I need constant on, I can just press and hold the momentary switch. For this reason, I prefer a momentary tail switch that is twisted for constant on.
I do want strobe up first for maximum OODA (Observe, Orient, Decide, Act) loop disruption and concealment of my movement.
Furthermore, a momentary only switch has much less danger of accidental activation when carried in a pocket with other junk. If it becomes pressed, it will shut off as soon as the pressure is released. If a clicky is accidently pressed, it stays on until I notice something getting hot in my pocket.
For an EDC light, I do like lower modes so that I do not have to use blinding, battery draining light output for the mundane tasks for which the light will be used most often. However, this is not an absolute necessity. I have usually carried a keychain light - currently a FourSevens Mini CR2 - as a backup light and for use when I do not need/want super high output.
Having said this, I have been carrying and using lights with forward clicky switches for some time without major issues. If the light does accidently click on, I can usually get it clicked off reasonably quickly.
After 15 years of carrying one Surefire or another, I am currently carrying a FourSevens Quark 123 Tactical (predecessor to the QT2L), set for strobe with the bezel tightened and high with the bezel loosened. This light has a partial shroud over the tail switch. I find that if my thumb overlaps the shroud on both sides of the tail switch, accidently clicking the light to constant on will usually be prevented.