Canon 24-70mm f/2.8L with cracked filter stuck on lense. Any ideas to remove?

Whether or not someone should use a "protective" filter is a different question then whether or not the filter will affect image quality.

Physics tells us that a filter will always affect image quality.  At best, it will be so little that the filter will cause no noticeable degradation.  At the worst, the filter will make  a very noticeable difference.  It all depends on the lens, filter, and shooting circumstances.  Anyone who tells you a filter "always" or "never" causes noticeable degradation is spouting superstition, not a rational opinion.

Physics also tells us that there are some circumstances where a filter can provide some useful physical protection.  Anyone who tells you that filters "always" or "never" save a lens is spouting a superstition, not a rational opinion.

The important questions to ask are how much image degradation and how much physical protection will you get in your circumstances.   Once you know this, you can make an informed decision if the protective benefits outweigh the image degradation in your circumstances.

Consider someone who will be running through the woods and feels uncomfortable with an exposed front element, but worries about missing a shot while removing a lens cap.  They have a choice of missing a shot due to lens cap use, or using a filter and risking a loss in image quality.

I am going to go out on a limb and suggest that an image with reduced image quality is preferable to an image of the back of your lens cap.

Where we get into trouble is the natural tendency for people to claim that their choices are the best choices for everyone else in all situations.  This is rarely the case.  My suggestion is that you ignore any filter advice that says you should "always" or "never" use filters.  Instead, look at discussions of what filters can and can't do, and then decide how that applies to your situation.

When you see conflicting advice, try to confirm on your own.  It's easy enough to put your camera on a tripod and take two images, one with and one without your filter.  Compare the two, and this will show you exactly how your filter affects your images in the tested circumstance.