- Institutionally, both organizations are remorseless about the deaths of victims
The NRA doesn't radicalize killers to murder people, nor have they personally committed murder for its "cause".  Remorse requires guilt.  ISIS is guilty of waging Jihad and killing innocent people.  The NRA has nothing to feel remorse over.

- Both use fear and intimidation to obtain their objectives
Fear?  Maybe, as it pertains to potential situations that require self defense using firearms, training, practice, and good judgment.  Intimidation?  Hardly!  Lobbying is about as close as that gets. 
The anti-gun crowd uses fear of guns and law abiding gun owners, fear of AR-15s, and fear of "good people snapping one day" to sell their ideology.  They also use intimidation, like releasing lists of gun owner's names to the Internet and threats of shooting those exercising legal open carry on the spot.

- Both assume their ideology is superior to the wishes of the majority of citizens
Assume?  History has PROVEN the right to bear arms is superior to suffering tyranny or becoming the victim of a crime.

- Both have intensely loyal followers
The same can be said of The Brady Campaign, Every Town/Bloomberg, Moms Demand Action, Gabby Gifford's & hubby's Americans for Responsible Solutions and every other anti-gun or anti-2A group that springs up.

- Both recruit and indoctrinate members who are ignorant of the basic facts
Unlike the anti-gun side, the NRA is in the business of educating not only members, but anyone serious about gun safety.  They set the standards for gun safety training in most states.  They train the trainers who train the concealed carriers and other gun owners so they can be responsible. "Indoctrination"?  Facts are the strength of the NRA.  When exposed to the truth, many anti-gunners reverse their ignorance-based beliefs and become in favor of private gun ownership.

- Both are relatively small organizations that have impact far beyond their size
I think the NRA has a mostly positive impact on gun safety and use, whereas ISIS has a 100% negative impact on the world.  Given that distinction, the rest of the characterization might be true.

- Neither organization will apologize for the harm they cause
That implies both have caused harm.  NRA has done more for firearm safety than any other US organization (perhaps the military being an exception).  The NRA also protects our freedom to continue to exercise the right to keep and bear arms.  I see nothing to apologize for, so this statement is a completely dishonest comparison.  ISIS, on the other hand, is doing what they and their interpretation of the Koran say they will do -- they are executing people in the name of Jihad.  They will never apologize for their acts until they decide what they have done was morally wrong.

NRA did not give weapons to ISIS, the Obama administration did.