Should everyone be trained in dual specialties?

It is a good Idea to do this. But only in fields that have similar duties. Since you mention ground and air cav's, they have similar backgrounds so they should know about how each other operate and to gain experience in something that you would not be used too.

In the AF, the only career fields that really cross over each other, is the aircraft maintenance fields. I was cut trained to be a crew chief as well as do my primary job on B-52's. I did not forget this training, but I was on fighters the rest of my career and did not get to use it much. I also trained a crew chief on removing and replacing a component of ours because we were short manned and it was beneficial to have them also trained on it.

So it really depends on what jobs that are similar to do this effectively. I know that in the Marines, everyone is rifleman first then their primary job is second.

No, absolutely not. If people want to do that, that's fine. I've done it myself....VOLUNTARILY... I didn't want to spend a career doing the first one the Army gave me. I did the second one out of convenience and to get a foot in the door. The third one is where I've wanted to be the whole time and thanks to contacts I made in the second one, I got it. Making it mandatory... I'll take the early out, kthxbai

I held 3 MOSs during my career and I will say that it most definitely was an advantage when I got into the more senior ranks, but I'm not sure that the military should REQUIRE multiple specialties. It could be extremely difficult to maintain a high degree of proficiency in multiple fields at the same time and it could also create a nightmare as far as assignments go.
Bottom line, good to have a more diverse background; but shouldn't be required to maintain proficiency in multiple specialties.

I'd say, make 'em learn their MOS! The problem that I see with holding multiple MOSs is that the soldier is usually only competent in one of them, if that. If it were a requirement to hold two, that could change. As it stands, if a soldier hold two MOSs he can get promoted based off his performance in his current MOS to an MOS where he is barely competent, and now in a leadership position. SGT Richard H., mentions an example of this in his comment.

I think the Army would be better served by raising the standards of MOS competency than by requiring soldiers to hold 2 MOSs.

For me, this is a no-brainer. As submariners, we were REQUIRED to earn our dolphins or leave the boat. Dolphins symbolize the training and knowledge that the wearer knew enough about every part of the sub to be useful in any part of the sub during a casualty.

Of course, I couldn't shoot torpedoes, but I knew how they worked, how they were used, and how to do damage control (e.g., fires, flooding and power supplies).

If you transferred from one class of sub to another (e.g., "boomer" to "fast attack"), you had to do it all over again.

Yes. Cross-training and familiarization is vital, but I don't think every mech infantry soldier needs to know how to change a track on an Abrams.

I think it could be useful if the dual specialties were related. Combat arms would be easier than support functions in its relation to other branches/specialties.

However, a Soldier probably shouldn't dabble in multiple specialties without first mastering their own. I would love to learn another job and be able to perform multiple jobs but I still have a lot to learn in my current MOS.

Everyone should be trained in general soldier tasks. The Warrior Task List pretty much identifies what should be trained on. There is no really an issue with cross training as most of us have done this in our career but it should not be used to hold a dual rating or two MOSs. You should be in one MOS and move up in it. If not you will see this being used to cherry pick promotions.

I would say yes, it is best to know more than one job