Why You Want to Play with Bad Players

One of the most familiar laments new players make? If they only played against better players, they wouldn't get sucked out on so much and they'd be able to make more money.
The flaw in this thinking should be fairly obvious. Bad players make mistakes; mistakes equal money.
Where the Money Comes From
When you're playing poker, you're hoping to make money. But where does this "money" come from?
From your opponent making mistakes - i.e. he calls too much before the flop, draws without getting the required odds, bluffs too often, etc.
These are all blunders that directly equate to more money for you. Conversely, of course, if you screw up less often on average than your opponents, you are also going to be making and saving money.
Which begs the question: Why would you want to play against good opponents?
Good opponents by definition are going to be making many fewer mistakes than their weaker counterparts. Fewer mistakes means less dead money.
This makes the game harder to play marked cards, not easier.
Flawed Thinking
Once you get to the stage of playing poker regularly, live or online, you'll hear the same things over and over again from players who just lost pots to bad plays.
"I just lost; I had AA and this idiot called my all-in with 7-4." Or "A good player would never do that." Or "I would have won the hand if he had just folded!

For sure. Getting called by 7-4o can be frustrating. But it's a good thing.

This is very flawed thinking. Yes, a good player likely would not have called an all-in with 7-4. You're right. But the majority of the time you do get called by a hand like 7-4, you will make money.
Thinking otherwise is "results oriented," which has no place in poker.
Against 7-4o your AA wins approximately 85% of the time. You want your opponents to make calls like that. Do the baby-genius math: This means they are only going to win 15% of the time.
The rest of the time they are donating their stack to you. Poker is all about the long run. Short-term results do not matter. Over the long run, if he makes that call every single time, you're going to be a very rich man.
"Good players are easier to read; you never know what a fish is thinking"
This is another one you hear all the time. If the players are really all that good, then you really shouldn't be able to read them anyway - but that discussion is for another day.
Although you might be able to understand a good marked cards lenses player's thinking with greater ease than you can read a fish's thoughts, that really doesn't matter.
Fish are going to make errors so often that you really don't need to "get into their minds." Instead, just wait for the nuts and value bet the crap out of them. Players who just call all the time are the easiest in the world to beat

The adage is true: you can't get blood from a stone.

When you play versus a competent opponent, things aren't quite that easy. They are only going to put money in when they think they have an edge. Thus, you need to read them because you need to know how they are playing against you.
The old adage is true: it's impossible to get blood from a stone. So why would you wish to play against a bunch of stones?
Remember, the more mistakes your opponents make the more money you are going to make. While fish may win pots in the short term with various bonehead plays, in the long run those same bonehead plays are going to be what make them losing players.
Don't worry about the short term; yes, playing with more bad players may increase your variance. But ultimately those are the most profitable games you can play in.