I wholeheartedly agree that the Democratic Party contains many different philosophies governing them and that this provides difficulties in getting legislation passed. I do, however, prefer it to the alternative of marginalizing members who disagree with one or two parts of the main platform in an effort to provide a façade that no one in the party disagrees on a single thing, ever. The Republican Party was very successful in doing this from the late 1980s until recently.

That said, I am rather cynical when it comes to politics. As Norm Coleman's chances of being re-elected grow ever slimmer and as the Democrats come one vote closer to winning a cloture vote all by themselves, people such as the Blue Dog Democrats being spearheaded by Senator Evan Bayh of Indiana see an opportunity to make a killing both for their states and politically in this session of Congress. It seems that they are threatening to block legislation by breaking away from the Democratic Party on key votes unless they get exactly what they want.

I think of it as the flip side to certain Republican governors turning down federal unemployment assistance. Sure, there may be problems with legislation, but instead of the boring and unassuming thing of doing their job and working on fixing it, they grandstand and threaten to torpedo it outright in an effort to score some cheap political points with their base/constituents.

As for the second part, "don't they realize change is hard," I'd say that they as career politicians don't want change. They like the status quo because they profit from it both politically and oftentimes, financially.

First, there are as many - possibly more - of Democratic political philosophies as there are Republican philosophies. From Blue Dog Democrats to those with socialist leanings, Democrats are noted for attacking their own. It's a spirited, semi-chaotic process. No eleventh commandment for them!
While it's sometimes unfair and harsh, I would rather see the scrutiny of policy from both within and outside the party. Policy needs examination and, if warranted, criticized to see what flaws might be there.
I don't think all of the Democrats are doing this. I'm not a Democrat, and when I talk with Democrats about Obama they're inclined to back him - and make decent arguments supporting his actions.