It happens every year: Somebody gets it in their head that the National League should add the designated hitter and writes a piece about it. The latest are Matt Eddy of Baseball America and Tim Heaney of Sports on Earth. The online community of writers and fans choose sides and it's brother against brother in a debate so bloody it makes cake vs. pie look like one of my daughter's tea parties.
One justification for the change is the notion that the National League clubs are at a competitive disadvantage in interleague play. That it's unfair (or simply nonsensical) for both leagues to be playing baseball according to different rules. There is also an aesthetic argument, as fans generally prefer watching someone who knows what to do with a bat in their hand to whatever this was:
Impact on MLB would be far greater than you realize
There are practical ramifications to expanding the designated hitter as well. Payrolls would increase, for instance, as older veterans whose defensive value was gone would be able to hang on later into their careers. We would also see the further proliferation of the deplorable 13 man pitching staff, since clubs would no longer have to burn through their bench options as pinch hitters. That would make it far easier for clubs to hold onto their Rule 5 draft picks for a full season. Finally, we would see an uptick in offense as these superior hitters and inferior pitchers were given increased exposure.
That said, I think we'd all adjust to the changes pretty quickly. We are all very used to the designated hitter now that it's middle aged, and I doubt it would impact our viewing experience much. Naturally, then, I am vehemently opposed to its expansion. I'm not concerned about these practical changes. I'm more concerned about what the designated hitter represents.
The DH in both leagues would change what MLB has always been
Once upon a time, there was a clear delineation between the American and the National Leagues. Of course, in the beginning, this was because the AL was an upstart rival to the NL's hegemony. When the leagues began to collaborate in the early 20th century, the changes made to the league structure (the World Series, the waiver system, etc), highlighted the distinctions between the two.
They had separate presidents and umpires, and were, administratively, entirely separate entities until the Black Sox scandal and the rise of Kennesaw Mountain Landis. Still, the leagues remained fairly distinct through rules designed to make trading players between the leagues difficult. If you were a Cardinal, for instance, you would more likely than not wind up being a National League guy for your entire career.
The implementation of the designated hitter in the American League was the last development to truly highlight this distinction. Since 1972, that distinctiveness has been gradually eroded. The league presidents and single-league umpires are gone. Interleague play is now simply a regular part of every team's schedule. Literally, the only identifiable difference left between the leagues is the designated hitter. Without it, the logical argument for even having two leagues at all falls apart. I'm not a strict traditionalist, but I do think keeping vestiges of baseball's more bifurcated past is a good thing.
Baseball is all about variety
After all, this is a sport that loves revels in preserving difference. Clubs are welcome to build their ballparks essentially to whatever specifications they want. Pitchers succeed with a variety of arsenals and hitters wait for their offerings in unique batting stances. More than any other sport, baseball rewards variety and that variety informs its charms. Standardization, on the other hand, is boring.
Sadly, I'm convinced that the introduction of the DH to the National League is inevitable, and once it's there it won't go away. The MLB Players Association would never consent to eliminating the designated hitter, and rejiggering rosters that contain one-dimensional sluggers like David Ortiz, Victor Martinez, Kendrys Morales, Billy Butler, and Kennys Vargas would essentially be impossible. Someday, in the near future, then, the articles about synergizing the leagues will finally end, and that will be the only positive to come out of it.