Most of the players that are above level 25 and have under-leveled subs are either lazy or careless. Those people should not be "carried" any further.
There are some that don't know any better. Then, the only way they find out is when someone /shouts: "Go level your subjob, you fucking noob!!" ...That's real nice to hear.
Here are a couple of stories that sort of relate...
A while back, I was soloing a bit in La Theine and there was a WAR soloing as well. He was level 20 and had no sub. I asked him, out of curiousity, why didn't he have his subjob yet?. He said he only partied once or twice and had a bad experience with the other players, each time. So he decided to just solo whenever he played. I told him that the jobs become much easier with a [properly leveled] subjob. I also offered to help get him the items needed and walk him through the quest. He declined and said he probably wasn't going to play the game much longer. I told him whenever he's on again, send me a /tell and I'll try to help him then. To which he replied, that he's not going to be playing at all any more and canceling his account. I haven't heard from him again.
On the other hand, one time I was getting ready to head out farming as a 50something DRG/15THF. While I was near the AH in Lower Jeuno, someone /checked me and said: "LOL... nobody is ever going to pick you for a party with that sub."
I replied: "Do you see my party flag up or a search comment that says I am looking for one?"
He says: "LOL.. No."
So I just said: "LOL then mind your fucking business!" and left it at that.
Anyways, I guess my "point" is... Ask, before you rip someone apart for being "gimp". Especially in the lower levels. Maybe they don't know the benefits or there may be a valid reason for it. Just yelling and humiliating them, won't help the matter.