Republicans not letting Democrats have a democratic vote.

Holding a fair democratic election is not an easy thing to achieve. But I have long suspected that the convoluted election process in USA is purposefully complex and full of little rules and exceptions here and there. After all, the harder it is to understand the process, the easier it is to manipulate by those in the know, so I get that.
I have a PhD myself and still it took me over an hour to understand how primaries work (even without all these niceties in rules). Only to realize that at the end of the day, 200 people in Washington (super-delegates) have about as much electoral power as 20 million "ordinary" people.
But has USA finally reached the point where the system is so ridiculous it stopped bearing any semblance to democracy? Here is the latest example which makes me inclined to think yes.

Clinton and Obama were close in primary race, with Obama having somewhat better momentum. A lot depended on Texas and Ohio primaries, where Obama win would seal his nomination and would let him start preparing to the actual presidential election. I believe odds were placed in his favor, too. Republican race was finished at that point, with McCain already having won his nomination.

Seems like a fairly innocent setup, but here is where all the little complexities arise: Ohio and Texas allow open primaries, i.e. anyone can come and vote, without registering with a party. And what happened is that a lot of republicans (who did not need to vote for McCain anymore) went to the democratic poll booth and voted as if they were democrats. They voted for the candidate who was behind (Clinton in this case) to make sure democrats continue to squabble, throw dirt at each other, and waste money, while McCain is gathering money and momentum.

So, what kind of election is that where a republican can come to a democratic primary and just mess with the results? What kind of vote is that where many people have incentive to vote for the 'bad' candidate, just to weaken the candidate they themselves consider 'strong'?