Zero. Not sure if you are honestly asking or if you are trying to ask why I seem to be contradicting you with confidence? I have worked in medical field since college and past 17 years with spine physicians (physiatrists, pain management, anesthesia), surgeons, physical therapist, chiropractors at a Spine center and now work with ortho surgeons along with more spine surgeons. I have worked with some pretty bright and talented people over the years. I also have lifted like crazy since a young age and developed a spine issue in which I have treated with diet, exercise, fasting and a whole lot of question seeking and finding answers through these avenues and other. I avoided medications and surgery with success.
Again, disagree. You have a dysfunction if leg raises increase your back pain. Yes, the illiopsoas and illiacus can compress your spine if they are tight along with pulling you vertebrae anteriorly yet if you have balanced strength with all surrounding stabilizers (glutei, lower abdomen, etc) along with adequately lengthened hip flexors then this should not be concern. If your pelvis is moving posteriorly then you glutes are weak and so is your lower abb.
Marching will increase low back pain if your glutes are weak, especially minimus and medius along with TFL. Marching is a great exercise for spine. Many elderly people do this frequently with success.
Glute kick backs need a properly strengthened core. A person should be able to isometrically control their abdomen and core prior to doing a dynamic movement involving extending the hip. Yes, if the core, low back and abs are weak then the kick but would be applying too much force for the core to control. So the idea would be to strengthen core prior to stabilize and absorb this force then progress to the kickback motion.
Back pain with exercise does not equal "sciatic" nerve being pinched. There are plenty of reasons a person can have back pain during exercise without the sciatic nerve being effected. A great percentage of people have herniated and bulging discs and never know it. Often people get MRIs and have several levels with degeneration yet not all of it contributes to their pain.