Pin on front sight bases were military spec for some reasons. First, they are tamper proof, Joe can't mess with them. If there is one thing GI Joe will do, is disassemble the gun past his level of operational maintenance and then screw it up putting it back together. That just creates more work for others and dead lines his gun on the spot - which may have been a quiet moment in a busy day of combat. And some would do that to get out of it.
Second, pins held the FSB on to resist torquing when a bayonet was attached. Most civilian shooters won't and don't need that level of retention. A barrel set up for set screw use usually has a detent ground in on the bottom surface of the barrel for the screw tip to fit into, and that has been doing a good job for quite some time on thousands of owner built rifles.
Because owners like to change things, a set screw or clamp on sight base allows easy changes in the future. And that is now under government control, as changes in ITAR regulations will require a gunsmith who alters the weapon by removing or installing pins to obtain a separate license, about $2500 a year. So, the price of working on them will go up. Even if we get the State department to back out of this, it still remains - a pinned sight is considered a permanent alteration. You do drill into the barrel and it does leave grooves in it, which may show if other changes are made later. Many owner builders avoid the extra work and complication. I, for one, changed up a build with handguards held on with a clamp on FSB and later installed a free float with optic. The cost was all in the parts with no gunsmith fees involved, done in less than half an hour.
Pins are permanent, but how we might want to change furniture on an AR isn't.
