HuffPo Pollster flags four separate posts with differing perspectives by Sam Wang, Jonathan Bernstein, Michael McDonald and John Sides on the effects of gerrymandering.
Sam Wang’s NYT op-ed explains gerrymandering as an exceptionally-effective form of disenfranchisement:

…Gerrymandering is a major form of disenfranchisement. In the seven states where Republicans redrew the districts, 16.7 million votes were cast for Republicans and 16.4 million votes were cast for Democrats. This elected 73 Republicans and 34 Democrats. Given the average percentage of the vote it takes to elect representatives elsewhere in the country, that combination would normally require only 14.7 million Democratic votes. Or put another way, 1.7 million votes (16.4 minus 14.7) were effectively packed into Democratic districts and wasted.
…Democrats would have had to win the popular vote by 7 percentage points to take control of the House the way that districts are now (assuming that votes shifted by a similar percentage across all districts). That’s an 8-point increase over what they would have had to do in 2010, and a margin that happens in only about one-third of Congressional elections.

Jonathan Bernstein takes issue with some of Wang’s reasoning. Foe example,

What really annoyed me about Wang’s case against gerrymandering is that he makes a point of bashing “ugly” districts — you know, the ones that have odd shapes, such as the one that gave gerrymanders their name in the first place. The piece is illustrated with some of them. What’s wrong with that? If districts are going to be “fair” to Democrats (that is, get the same ratio of seats as votes), then because of where Democrats and Republicans live it’s precisely the value of having “pretty” (compact, regular-shaped) districts that’s going to be violated. Under current conditions, compact, regular districts strongly tend to favor Republicans. One can argue for them anyway, but anyone who cares more about partisan “fairness” shouldn’t also be playing up the importance of “pretty” districts. Well, to my tastes no one should care about compactness; there’s simply no reason, in my view, to care about the shape of districts, all else equal. But at the very least, anyone complaining about ugly districts should know the very predictable effects of compactness.

John Sides argues at Wonkblog that voting behavior is not about gerrymandering so much as it is about political party:

…The most important influence on how members of Congress vote is not their constituents, but their party. This makes them out-of-step not only with the average American — the “broad-based public opinion” that Obama mentioned — but also, and ironically, with even their base. Members are more partisan than even voters in their party….Democrats and Republicans are just polarized, no matter whether their district is red, blue or purple. It’s hard to imagine that creating more competitive districts will mitigate polarization. Members in purple districts are pretty polarized, too.

Of course there is a counter-argument that the point is not that gerrymandering determines voting behavior. Rather, gerrymandering is about herding party supporters into compact districts to dilute the effects of their voting power. Michael McDonald tweets at Elect Project, “Gerrymandering deniers: new research published soon shows compact districts = less biased plans.” He responds to Sides that ” I agree a small bias favoring Rs among compact districts – including VRA constraint – but R gerrymandering well beyond this.
It’s an interesting debate. But it’s important to note that none of the four participants are arguing that districts could not be made more fair. Certainly, Democrats have nothing to lose by fighting for a more even-handed approach to congressional redistricting.