Read other letters about this article
First of all, its a myth to say that no one is based on Clinton based on ideals. For some she is better ideally suited to fight the G.O.P Machine (whatever that is). For some, they have made an idealistic choice to rule out Obama because of his Reagan remarks, or because they think he's a political lightweight.
Pragmatism can lie on both sides of the street in this debate.
Further you uphold the Democratic Party values as "ideals" to vote for. Some of those Obama supporters are not members of the party, so how are you going to convince them to vote for ideals they don't have--for a candidate (Clinton) who many of them--particularly after the way Clinton has been conducting her campaign--do not like. Many (increasing numbers of) Americans vote for a person and not a party in elections. Thus the results of elections are so hard to predict.
Finally, your point about Republicans in the white house. Some American people are going to see George W. Bush as the problem, not the Republican party as a whole. Because you are a party loyalists, this may be difficult for you to understand, but like I say, many Americans (even Americans I know and love) think of personality first and party second. George W. Bush is not running in 2008. I know some people who "hate" him and yet are going to consider the next Republican candidate as an individual, not necessarily as a Republican, and therefore another Bush.
Party Democrats need to consider the way people make decisions in these elections as they choose their candidate. Party politics don't matter for a lot of people--as we've seen in the past three elections since Nader entered the fray. Many people actively think the Democratic Party is weak for not standing up to Bush (consider the current Congress and the front-runners). Whatever values it used to hold seem pretty watered down in its main contenders.
These are just things I think a lot of voters, pragmatic voters, are going to be considering. You can't throw it all at the door of so-called "idealism."