Is the Scandinavian overly unsound?

At least at the beginner/intermediate level, the Scandinavian is just a terrible idea. The most rational move is to take the pawn. If 2. Qxd5 (Mieses-Kotrč) then just getting the knight out is already pressing the queen. The Queen either has to move to a8 where it has no real say in what's developing or it moves almost all the way back and just gives the knight free development.

The Modern variation of the Scandinavian looks better, delaying the taking of the pawn with 2. Nf6. At that point the pawn can be safely taken back, with 3. Nc3 still offering a knight trade, but at that point nothing can immediately and safely threaten your Queen, giving you time to develop pieces to back it up and give you an advantage. However I'm still not sure how sound this is. Of course I'm only looking at 2. exd5, but that's the only rational move I see against the Scandinavian. Am I not seeing something or is this defense genuinely terrible?

It's a perfectly fine opening for black. Bent Larsen played it against Karpov, Anand played it against Kasparov, Carlsen played it against Caruana twice, in 2014. and 2016. Though it's not that popular at the highest level, it's fine.

This defence has been played by masters of the game for 175 years. It is still around. A casual "it looks bad" take after three moves is not enough to form a judgment on this opening.

I have Mattias Wahl's book, and have looked up various players on here who play this and speak about it a lot in these forums.

I think that it's kind of dodgy. Having looked at the games, people don't seem to realize the lines to play up until 2000 or so.

Your choice. I decided not.

If both players are rated under 1000 then the opening is the least of their concerns. 

Although true, obviously everyone needs to make a first move.

Would you recommend 1...d5?

Sure, why not? The OP is an 800 player...to them I would say just choose one of the main openings to play and explore for a period of time, it doesn't matter which. 

Yeah. I can understand his query though. Most people are looking for a low maintenance opening, and that they won't need to learn anything else.

Not sure that the Scandi is that.

Of course, but it must be understood that this is not really how it works if you want to get serious about learning and improving. Of all the major openings, Scandinavian is probably one of, if not the lowest maintenance so for the purposes of getting a playable position out of the opening game after game it's probably a good choice. I suspect though that the OP has done little to zero actual research into the opening. For example, in the opening post the OP is questioning 2.Qxd5 for black because 3.Nc3 hits the queen. Even the most basic introduction book/video to the Scandinavian will address this obvious move for white and explain why it is not the loss of tempo that it perhaps appears to be at first glance. 

honestly, for me the scandi isn't for beginner when you play it as black.

They are a lot of trap and your position can be really hard to deal for black if they don't know what they are doing .

this opening seem simple but aren't .