Opening for Black Pieces

One thing about the French is that you can transpose into a Sicilian against 2.Nf3 or 3.Nc3. I like to do this as not only is it good to learn another opening but it avoids the exchange

There is no such principle.

Maybe you can formulate something for the f-pawn (a more refined version of Finegold's "Never play f6"), but the c-pawn is moved in practically every normal opening.

#23
That is not my formulation, it is one of the 4 opening principles formulated by Lasker.
Grandmasters violate all 4 principles, but that does not mean it is OK for John Doe too.

There has to be a specific reason though. In general, you shouldn't but if there is a very good reason, then do it

#25
If you follow all 4 opening principles, then you get sound, playable positions.
If you violate any of the 4 principles, then you will meet problems, which you may or may not overcome.

Lasker was wrong when he stated you should only play e- and d-pawn openings. Lasker played in a completely different time in chess, where playing dynamic chess (like Chigorin would do) was actively frowned upon. 

The right principle is for black to try and prevent the e4 and d4 pawn-center for white. 1. ...c5 prevents d4, so that's fine. 1. ...c6 and 2. ...d5 is also okay, as black immediately destroys the e4-d4 pawn center if white plays 2. d4, but I would rate it as more difficult to play for a beginner.

#27
Lasker played by the same rules as we play now. His 4 principles were very deeply thought of. None of his 4 principles are 'wrong' by any means, but they have exceptions.

Black can allow the pawn center e4 d4 for white and does so in many openings: King's Indian Defence, Grünfeld Indian Defence, Pirc Defence... It is possible, but it is hard to play.

1...c5 does not prevent d4: white usually plays d4 anyway and then gets a centralised knight on d4 instead of a pawn. Black has a long term endgame advantage as he has one more central pawn and the open c-file, but has to defend against attacks based on white's better development and center control, i.e. white plays dynamic chess and black bets on his static advantage.

For a beginner as well as World Championship contenders 1...e5 is simpler than 1...c5, 1...e6, 1...c6, though it does not matter as both players will blunder anyway.

Lasker also lived in a time when most master games started with 1. d4 d5 2. c4. Including most of Lasker's games.

Even if he wrote down those principles in some book for beginners, we should not take those too seriously.

#29
No, Lasker played Ruy Lopez most and that is still most popular at top level today.
https://www.chessgames.com/perl/chessplayer?pid=19149

He wrote this in "Common Sense in Chess" and all of us below grandmaster level should take that to heart. He was World Champion for 27 years, a record to this day. He is ranked as the #4 player of all time. Who are you to not take him too seriously?

Excuse me?

In the Spanish (or Ruy Lopez), first white then also black move their c-pawn in the opening. That was so in Lasker's time and also today.

Lasker must have been a giant troll to write down something blatantly false as a "principle".

I simply stated that needing to only play the d- or e-pawn is wrong. That statement by Lasker was wrong, as is seen by the flight of the Sicilian defence that came after his time. 

When I state that white wants to have the e4 and d4 center and black wants to prevent this, I am of course aware that there are exceptions. Hypermodern openings, like the Reti, think differently about this goal. Your examples however prove my point that black wants to prevent the e4-d4 center. In the Pirc and in the KID, black initially might allow this center to form, but then chooses to attack it immediately. In the Gruenfeld you see this response too, even though the Gruenfeld could be classified as an exception to the general principles of not wanting to hand over the center to white. That's chess however. For every rule there is an exception. However, those are not important for lower rated players. 

1. ... c5 prevents the formation of the e4-d4 center. If white perseveres with 2. c3 black will attack to prevent it forming with 2. ... Nf6 or 2. ..d5. Sure, white might play d4 anyway in the open Sicilian, but black will take it with cxd4 preventing white from getting the e4-d4 center. It doesn't matter that white gets to play Nxd4, that's not a pawn. Black is fine with giving a small center to white if he also can have some influence. 

I find that 1. e4 e5 is not at all simpler. Not for me anyway. There are many, many tactics out there in those lines. Many different traps. And then if you get a quiet Italian game, the middlegames are terribly difficult to understand. I think it was Seirawan who also stated he didn't really understand those 1. e4 e5 structures either. If that is the case, how can it be easier for beginners. Now after 1. ...c5 I can find plans much more easily.

I

#33
Lasker himself also played the Sicilian Defence, Sveshnikov Variation then known as Lasker-Pelikan. Not so in important games.
His recommendation is still sound, common sense.
Carlsen considers 1 e4 e5 as the best and Caruana and Nepo apparently thought the same.
It is most easy to explain to a beginner.

#32
So Lasker is a troll  and magipi is a World Champion?

No.

But when a world champion says something that is contrary to common sense, his own practice and all the other master's practice, we can safely disregard it as an oddity. This "principle" is complete nonsense, no matter from what angle you are looking at it.

I feel like I don't have a clear plan of response to what white is doing when im playing the sicillian. I feel too cramped and end up getting out traded or out positioned early on and the game inevitably ends up being me down material and more often than not losing. If I win, I never understand how or why i've managed to pull it off at least when playing the Sicillian. 

#38
In the Sicilian white attacks because of his development advantage and his control over the center. Black defends and counts on his long term endgame advantage as he has one more central pawn.

#37

World champion Lasker wrote what is common sense: "Common Sense in Chess"
It is completely according to his own practice. As white he played the exchange variation of the Ruy Lopez, to punish the tempo loss 3...a6 moving another pawn than the d- and e-pawn. As black he avoided 3...a6 and played the Berlin. It is even consistent with the practice of modern grandmasters. Look at the Ruy Lopez games of the recent Carlsen-Nepo World Championship match. In what games did they play other pawns than d- and e-pawns in the opening phase and on what move?

You can disregard as you want, but do not tell people that common sense is 'oddity' or 'nonsense'.