With respect to the weight issue, and I would add the related issue of overburdening a rifle by tacking on various appurtenances:
Wouldn't one obvious solution be to properly design the weapon system carried by the infanteer so the all the various sighting systems, aiming aids, spotlights, radar warning receivers ..... are properly sized and integrated so that they don't have to be bodged up in the field?
Some of the weapons that I have seen you guys running around with would make Rube Goldberg blush. Don't they upset the balance of the weapon?
If the bayonet lug were exposed and available, traditionalist that I am, I would certainly be inclined to carry the bayonet.
No matter how many mags you carry you will always reach the point where the "Plumber's Nightmare" you are carrying is nothing more than a club, a blunt instrument. The bayonet will always make that "club" a more effective weapon.
With respect to the issue of French and Russians not employing "Steel" when they had the opportunity:
Perhaps that is as much a matter of military culture and Tactics, Training and Procedures as anything else. Unless a force is trained to use a weapon, and becomes comfortable with it, and expects to use it and, in the case of the bayonet, becomes eager to use it, it will never magically clear the enemy from the field just by deploying it. The enemy has to believe that the wielder really wants to use it and that they are good with it.
The 18th and 19th century Brits developed that reputation. Other nations not so much. Even in the US Civil War there was a difference between the two sides in their attitudes to the bayonet. Reputedly the Southerners were much less eager to engage with the bayonet than the Northerners.
So, Wonderbread, I actually end up siding with your point, if you have no intention of using a bayonet, and the other side knows that you have no skills or capabilities in that regard, solely due to a lack of practice - nothing else is intended there, then far better to bring the Swiss Army knife and leave the bayonet at home.
Cheers, Chris