Arrogance or experience?
I love playing with my m14 too, but as a mechanic, I can honestly say I get plenty of business fixing mistakes that DIY'rs make.
Lots of non-intrusive straight forward stuff can be done by jo blo tinkerer. Maybe some of it is useless and overrated but I prefer my rifle to be tight as f*** regardless of group size.
Gas system welding should probably be done properly by someone experienced if at all.
To paraphrase what hungry said at his m14 clinic, The americans fought a (part of a) war with their loosey goosey m14s and they did just fine.
I think what he's not understanding is that I don't disagree that lots of people can place 3 tack welds. The issue is to know what else needs to be done to make that a modification that adds value.
The unitization mod is typically done to ensure that when the barrel twists, the band and ferule relationship remains consistent from shot to shot (barrels actually "twist" when the gun is fired, whipping circularly, and then elastically returning to their starting position).
A well set up M14 with a unitized gas system will have the bottom of the barrel band in full contact with the tip of the stock ferrule around the full circumference of the lower band lip. Realistically this can only be done properly when the stock is also bedded.
Also, you don't want the shaft of the gas cylinder to touch the stock band. This is why it's ground 20 thou oversized before you weld (or screw) the band in place. These parts will heat up and you don't want the cylinder to exert pressure through thermal expansion on the relationship between the band and the stock tip. I should also mention, you have to adjust the tabs on the bottom of the band to keep the handguard from putting any pressure on the stock.
A LOT of guys also believe you should shim the gas system. Shimming was invented for people who wanted to spend $10 on shims instead of paying for a unitizing job, which is beyond the reach of anyone that has no access to a TIG welder (or a milling machine and acetylene torch for spot-annealing if doing glue/screw). A shimmed system gives pretty good results, though not as good as unitizing. A unitized gas system no longer relies on the barrel shoulder to hold the stock band in place and is held fast by the gas lock. Using shims with a unitized gas system adds unwanted stress at the back of the gas system that will shift POI when the barrel gets hot. I would not recommend using shims with a unitized cylinder.
A properly unitized gas system is nirvana. A shims-only gas system is not as consistent, and the GI setup is the least effective configuration.
Remember though... to get the most out of a unitized system, you also want a bedded stock set up so that the stock ferrule puts upward pressure on the tip of the stock at the ferrule. This helps ensure the stock to band alignment returns to the same position after the impulse from each shot.