Presumption of innocence is only a thing for criminal cases. Civil cases use the balance of probabilities. To win there, you don't have to prove your case beyond a reasonable doubt, just that your version of events is more likely to be true than than your opponent's, however slightly.
Requiring plaintiffs to maintain a budget to pay fees would shut a lot of people out of the legal system, like individuals, for example. It would make it easy for large companies to violate the rights of IP holders.
And if a lawsuit really defames a defendant, after winning they can always turn around and file a defamation lawsuit.
"Ei incumbit probatio qui." I know it's not the case for civilian law in the US. I was only pointing out strategies for change.
Your point about plaintiffs with small budgets is an interesting one. Do you have examples of a David (individual) successfully suing Goliath over patents?
Burdening the system with more lawsuits isn't necessary if you immediately get a yellow card when committing a schwalbe. :-)
Not sure why you ask though. Are you getting at that looking out for small plaintiffs is a waste of time if they never win anyways? Because I don't think that's a good road to go down.
To address your last point, defamation is something that has to be proven in the US, and the standards for it are quite high (compared to the UK, for example, at least). A defendant can't attempt to argue and prove damages caused by the plaintiff without filing a countersuit, so I'm not sure how courts could go about handing out "yellow cards."
Requiring plaintiffs to maintain a budget to pay fees would shut a lot of people out of the legal system, like individuals, for example. It would make it easy for large companies to violate the rights of IP holders.
And if a lawsuit really defames a defendant, after winning they can always turn around and file a defamation lawsuit.