Whether or not there was electoral fraud, and whether or not it was enough to change the outcome, it remains an undisputed fact that the election was close. Both democrats and republicans turned out in large numbers, and the vote was roughly split between the two candidates. Nobody is alleging that a small minority Bush camp stole the elections outright.
It's also true that there is little evidence of electoral fraud, other than the discrepancy between exit polls and electoral outcome. That could be explained by other factors (republicans feeling a backlash against their choices). Certainly, starting from a position of trust, there would be relatively little motivation consider electoral fraud.
But we're not starting from a position of trust when it comes to electronic voting. Just as there is no evidence of it being unfair, there's no evidence that it is fair. There is simply no evidence as to whether it is fair or not, except the reassurances of the manufacturers. So-called expert claims that the election has gone "smoothly" or without "evidence of tampering" are meaningless - it would look that way whether it was tampered or not. The "debunking" papers provided by Diebold do not address this issue, and it is irresponsible for experts to comment on the "success" of the election while that issue is unresolved. The technical reliability of the machines was not in doubt.
We're used to trusting computers with our welfare and our life, and that's perfectly reasonable. They're very reliable machines. But when we trust a banking system or an aircraft's auto-land ability we're not just trusting the machine. We trust that the people who programmed it fully intended to make it function fairly and safely. Such trust is well placed because banks and aircraft manufacturers are motivated accordingly.
In the case of the voting machines, the allegation is that the manufacturers (either at a management level or at some lower technical level) deliberately rigged the voting software to favour one party. It is certainly possible to do that without being detected, and politically this seems conceivable at least to some significant portion of US citizens. Since the government isn't able to prove its legitimacy on demand, these US citizens would in theory be justified not to accept its authority, rise up in arms against it, or whatever their constitution says they ought to do under such circumstances.
The only reasonable remedies I can see are either to provide a voting system that leaves an unquestionable trail immune to tampering by an insider (which may end up being an old fashioned paper system, as it is in most advanced countries, for that reason) or to establish that the overwhelming majority of informed US citizens trusts the voting machine company. I fear that in fact what's happening is the US is being pushed down the second path without the "informed" bit.