I am aware that a great deal of what the SF do is indeed classified and for obviously very good reasons. And I am not saying that Line Battalions should fully replace SF, by no means, and certainly not that SF are just well-trained Light Infantry. But I am saying that much of the skills levels - though not all the specific skills, let alone all the roles performed by SF - should be integral to US Army infantry units. Your terms of reference seem to be framed by US Army practice; such practice is not universal by any means.

For example, in the US Army, the Scout Platoon of an Infantry Battalion performs conventional reconnaissance, surveillance, and screening/security tasks for its parent Battalion; a LRS Det or Company handles both the LRRP (to some degree anyway) and surveillance tasks for the Battalion's parent Formation. In The RCR, the Battalion Reconnaissance Platoon (including snipers) had to be, and was, trained and equipped for both roles - tactical and operational reconnaissance tasks of all manner - as well as HUMINT; and whether that meant operating strictly on foot, helicopter, using an assault boat from an O-Class sub (no longer in service - that was a while ago now), or from the back of a Lynx, or whatever, then that's what was done, mission-dependent.

An Infantry Battalion could perform a number of other unconventional tasks. Providing bodyguards for domestic and foreign VIPs, for one - done out of hide - training taken at either Chichester or the Secret Service course in Virginia (a buddy of mine was one of the guys who got the tap for that). A great deal of the Combat Swimmer role was performed either by Pathfinders (not quite the same as their US Army counterparts) or by Combat Engineers. For other, more "strategic" tasks, individuals or certain groups were likewise tapped on the shoulder and received the requisite training (if it was lacking) and detached out of the Battalion to attend to their duties. Since SF have been formally brought back (starting in '92) in the Canadian Army, some of this has since changed. An Infantry Battalion is not an SF Unit, nor am I arguing that it should be; but a well-trained Infantry Battalion is capable of a surprising range of SOF missions, and regular Infantrymen should be, and can be, trainend accordingly.

What I am trying to point out here is that outside of the US Army, there are several Armies where the distinction between Main Forces and SOF becomes decidely blurred. Which is one of the reason why Commonwealth forces prefer SAS and Delta-type SF to handle full-fledged SF missions and tasks, and let the regular battalions handle the stuff on the outer fringers (somewhat as the Rangers do in the US). Many SF units do not have the time to conduct all the myriad missions, some of which are at cross-purposes from a Unit-training standpoint. It's not unknown for one mission or task or set thereof to take up so much time that another becomes neglected, but that's sometimes because a Government sets policies and makes committments - especially to other Governments or actors - that strain available troops and resources.

As SF don't always have enough time to handle all the missions that their Governments thrust upon them, letting Line Battalions train to standards (though anything like the full skill sets) approaching that of SF makes for far more capable and flexible Line Infantry that may be able to relief SF of some of the "fuzzier" stuff on the blurry line that distinguishes between SF and Main Forces, while at the same time making for regular units that are genuinely capable in the "Full Spectrum" of Operations - not like what happened in 2003, when after crushing the Iraqi Armed Forces, the US Army had to re-learn COIN almost from scratch. It did not have to be that way.

If many people, even within the US Army, look down somewhat at regular US infantry and deride them in terms not far removed from the draftee armies of the past, it's not because the US Infantryman is not capable of being more or less of Ranger-quality. It's because the Army, for various reasons, won't let them.

And this is where the present structure of the US Army SF may in some ways be problematic. "Delta" or whatever it's called these days, represents one of the high-ends of US SOF - comparable to the SAS, etc. But the rest of the Army SF (I'm just talking about the SFGs, not CA, PsyOps, et al.) has no parallels in the English-speaking world at present, or even in much of the rest of the world. In the rest of the English-speaking world, the missions that the Green Berets (exclusive of Delta here) perform are divvied up between an SAS-type SF and the regular infantry, with perhaps a few Commando Forces units for more specialized roles (particularly parachuting and mountain warfare).

Strategic Reconnaissance - amongst other missions, is certainly best handled by a dedicated SF unit. No arguments there. But I suspect that Government policy drives a demand for SF aside from SAS-type units to an extent that may be unnecessary. And some other missions presently handled by SF may be handled quite well by highly-trained infantry battalions.