Curious about this line. Why only against the SB? I know you are talking about blind vs blind, but if someone is folding into the CO or BU, they are still going to raise, and in my opinion you're as better off holding KJ or QJ against them than you are against SB (granted, you will probably be on a 3-handed pot, but this is what I think. Besides, your steal equity would not go down very much, since both SB and BU/CO would have wide ranges here, and if you flop a good hand... then better. Having two people in the pot with you also increases your implied and pot odds, which is good for JQs since you'll be getting some draws with it fairly often. But I don't know, in a 3-way pot, I can't stand my ground very much
guess it kinda depends in their range quite a lot).
Anyways, answering the thread's question, JQs and KJo are a fold from Early Position. Basically, entering in a pot EP by calling without intending to trap (say, you have a very strong holding and you want to get a loose-aggressive opponent to open, but this is a very risky and tricky play) is an awful play. You should always raise from Early Position, and have a hand strong enough to do so, since you will be playing OOP in what will most likely be a multi-way pot.
One of the reasons for this is, like it was mentioned above, that you have no clue whether someone behind you will raise, and you will most likely be forced into a fold face 1 or more raises. You are also getting into a pot with a speculative hand OOP and with no initiative (meaning: you will rarely catch a good flop, and when you don't catch it, you won't be able to steal the pot away).
Not only that, but you also don't know how many callers you will get. KJo is a hand that is overrated and hits pretty rarely (and almost never hits strongly enough). With KJ your point should be to get into a pot In Position via a raise (so you keep initiative) against 1 or 2 opponents capable of letting their hand go, so you can sometimes steal to balance the times you hit. With QJs you at least want some callers to call with you pre-flop, even if you don't want to raise with it. So, even if you miss and aren't able to steal, with more callers you have greater odds to pay that off the times you do make a great hand post-flop.