"But having to prove intent makes it harder to get convictions!"

So does the rest of the Constitution, which is why every part of it has been under attack.  After all, if they can jail you when you didn't even know there was a law, let alone intend to violate it, it's easier to control people.
...FBI Director James Comey differentiated her "extremely careless" handling of "very sensitive, highly classified information" from other cases involving "intentional and willful mishandling."

Not everyone gets the benefit of such distinctions. Consider the retiree on a snowmobile outing in Colorado who got lost in a blizzard and unwittingly crossed into a National Forest Wilderness Area; the Native Alaskan trapper who sold 10 sea otters to a buyer he mistakenly believed was also a Native Alaskan; and the 11-year-old Virginia girl who rescued a baby woodpecker from her cat.

The first two incidents resulted in misdemeanor and felony convictions, respectively, while the third led to a fine (later rescinded) and threats of prosecution. All three qualify as federal crimes, even though the perpetrators had no idea they were breaking the law.

The federal code contains something like 5,000 criminal statutes and describes an estimated 30,000 regulatory violations that can be treated as crimes. The fact that no one knows the precise numbers is itself a scandal, compounded by the fact that many of these provisions include minimal or no mens rea requirements, which ask prosecutors to demonstrate that an offender knew he was doing something wrong.
"But that means doing actual work! And actually proving things!  That's hard!"
Sooner or later some bastard in Congress is going to propose ignoring the 4th and 5th Amendments 'in cases of great danger/security risk/importance', because having to actually obey the law gets in the way of convicting someone.

Yet Senate Democrats dismiss the proposed changes as "corporate protection." Their chief complaint is that requiring the government to prove a defendant knew he was breaking the law will make it harder to convict people.

No kidding. The same could be said of many safeguards widely supported by civil libertarians, including the presumption of innocence, the requirement of proof beyond a reasonable doubt, and the ban on double jeopardy.

Guilty people, including violent criminals, surely escape conviction because of these rules. Likewise, if Congress beefed up federal mens rea requirements, some white-collar malefactors and felonious fat cats probably would escape criminal punishment as a result. But that prospect should not deter Congress from doing what's right.
'Doing what's right' would've involved, to pick one, a REAL investigation into Fast & Furious(and the other gunrunning operations), and people being fired, and charged, and tried.  We saw just what 'doing what's right' means to far too many in Congress: nothing.