Civilian vs Professional

It is absolutely 100% true that professionals (security, law enforcement and military,) often have a lot of experience putting their hands on people and thus have a very good sense of what techniques will actually work in a fight and which ones will not. However bad self defense advice begins when professionals forget the advantages they have over civilians.

Professional advantages:

1. Professionals have a legal responsibility to protect people or property, and do not have to justify their involvement because it is their job to be involved.
2. Professionals have an obligation to neutralize the problem causing individuals, usually by apprehending them.
3. Professionals have a set of tools and resources provided to them by their job descriptions and employers. This includes hand cuffs, tasers, pepper spray, guns, uniforms, established duties, training and legal protection.
4. Professionals have an established support team to help them.

Civilian disadvantages:

1. A civilian's primary objective is usually rapid escape, and they are more likely to be viewed as a trouble maker engaging in brawls than a hero doing their job the longer the fight continues.
2. The civilian's goal is survival and reduction of inconvenience, not capturing bad guys.
3. When a civilian employs any self defense tool he has no employer, uniform, established protocol or legal team to back him up in court. 
4. Civilians are usually on their own. When a civilian pins an attacker, it's just as likely more attackers will arrive as it is help will arrive first.

One example of fairly misguided advice I hear is "no one is getting in a one on one knife fight outside of Westside Story." This makes sense to professionals who either aren't allowed to carry a knife on the job themselves, OR who themselves carry a firearm on the job. From the professional perspective knife fights are most likely to happen in prison, with one person having a shank and the other person being assassinated, because the shank is the most likely weapon to be employed in that environment, and shanks are rare enough there that it is unlikely the defender will have one on hand. From the professional perspective there will only be one knife in the fight, never two, and it will be against someone with no weapon at all or someone with a gun. 

Yet carrying knives with civilians on the street is common because knives have very real utility outside of self defense. Knife duels are so common with civilians that one security-related team I was on broke up or investigated multiple knife duels over the course of a few years... in that public outdoor setting a one on one knife duel was more likely than one unarmed individual getting attacked by a knife. The street is not prison, it is often possible to deploy a knife as you see trouble coming, and that trouble's plan of attack very well may be trying to stab you. It is all fine and good to own guns, but when emergent circumstances arise the average person is going to access a box cutter, kitchen knife or folder a hundred times faster than a firearm.

The most important example however in this age of MMA, is the advice professionals are giving out about what martial arts to study. Grappling arts where the focus is on taking down and controlling the opponents are ideal for most professionals. The professional is being paid to be there all night anyways, and the assumption is going to be that the professional was doing the right thing. The professional has help coming so that the longer the physical confrontation lasts, the more likely it is to end in their favor. 

Grappling arts do not have this same appeal to civilians. The longer a civilian is entangled with an attacker on the ground, the more likely his whole night is going to be ruined by police reports, and the more likely he is to have to take time off of work to have to testify in court in the future. The longer the physical confrontation continues for the civilian, the more likely the attacker's friends are to show up and make the situation much worse for the civilian.

It is no wonder then why striking arts and weapon arts are more popular with civilians. The footwork practiced in almost every striking or weapon art is potentially evasive and can help the civilian escape faster. The clinch work practiced in most striking or weapon arts focus on the civilian trying to stay on their feet and mobile. The civilian wants to KO, slow, and/or outrun the attacker rather than apprehend or submit the attacker. 

There is a certain subset of grappling that is extremely valuable to civilians, but as far as I can tell is not widely available to civilians. In MMA this type of grappling is the sprawls and getting up to your feet as practiced by Sprawl & Brawl fighters. Most grappling arts practice techniques that can potentially be used for this strategy, but they never practice this strategy, and without practice that strategy will not materialize in a real self defense situation.