How exactly does plea-bargaining do that? Prosecutors don't determine sentences; judges do, and the sentences they choose are circumscribed by very detailed guidelines.
[1]: http://blogs.law.harvard.edu/philg/2013/01/15/plea-bargainin...
An interview with Aaron Swartz‘s defense attorney reveals that, though the government was threatening Aaron with between 30 and 50 years in prison if he went to trial and was convicted.
Not only was Swartz not threatened with 30 years, but the prosecutors themselves threatened him with (an itself implausible) single-digit-year sentence. Swartz's own attorney thought it likely that even were he convicted, he wouldn't end up serving a custodial sentence.
It sucks when this case gets brought up, because the only way to get to the truth of it requires people to sound like they're defending Steve Heymann, the prosecutor in the case. There was a great deal wrong with the case. It's just that a 30-year sentence wasn't part of it.
"If convicted on these charges, SWARTZ faces up to 35 years in prison, to be followed by three years of supervised release, restitution, forfeiture and a fine of up to $1 million." (http://www.justice.gov/usao/ma/news/2011/July/SwartzAaronPR....)
Not pleading out would mean that the offer of a lower sentence is off the table, and the prosecutor would push for the threatened maximum sentence.