Here's my main reasons to be negative on Hillary Clinton.
1) Her M.O. for denying these allegations has already been disclosed (See all of the instances that she was actually caught lying in the past) and it is in play again with current allegations.
The M.O. includes (1) denying facts, releasing modifying explanations as new facts/evidence is public (2) attacking opponents, (3) playing victim to vast right wing conspiracy, (4) slow-playing evidence production, and (5) persuading people to plead-5th/refuse to testify. If you can't see through her attempts to cover up the recent allegations, you are willfully blind. I have no idea if she's actually telling the truth this time around, but she's using the same MO to hide her previous misdeeds, which were uncovered too late.
One example: (1) She made $100,000 from $1,000 trading cattle futures as a novice. Independent studies show that this was 1,000,000,000,000 to 1 odds to be that successful. Her initial statement was that she made informed decisions by herself based off reading the WSJ. New facts come up that she was associated with a head attorney associated with Tyson meat processing. Nearly 5 years later, she modified the facts, saying that she actually had a friend assist her in making trading decisions. This whole thing was likely a bribe, structured as placing bets on the future's market in trade for political favors that her husband (the Alabama governor) would give to Tyson (an Alabama company). Everyone else associated with these trades was prosecuted and jailed.
Compare that to her ever-morphing statements: (i) I never sent classified emails, (intervening fact: she sent 1000s of classified emails) to (ii) I never sent emails that were marked as classified, (intervening fact: she sent 100s of emails that had some classification markings) to (iii) I don't know what classified markings are, remember I hit my head and have a fuzzy memory, (intervening fact: her animated corpse being dragged into a van) to (iv) How dare you question my health and capacity to be a president, you right wing conspiracy sexist A-holes.
2) She operates under an elite group-think attitude, has proven that she lacks the judgement to make the right decisions and fails to surround herself with people that can stand up to her when she's wrong.
Case in point, she fails to appreciate the damage that hacking can have, especially when handling classified material, which by definition causes danger to national security if disclosed to uncleared sources and handled in non-secure means. She had TS/SCI (I had this clearance, you don't F around with this level of classification) on her non-secure private computer. She valued her own privacy over national security.
She also had 2 IT staffers try to bring to her attention that use of her private email server as against the law. Those staffers were told that (i) the email was authorized (Patently FALSE), and (ii) never ask about it again.
This attitude is the same attitude that resulted in the space shuttle exploding. Engineers had evidence that the O-Rings would fail, but it was deemed politically important to launch the shuttle. The people with the right answer were told to shut the F up, and they had to sit down and watch several astronauts and a private citizen school teacher die.
Yes, but that's not the equivalent to politics.... What about Iraq having WMD and a war being needed in 2003? Everyone swallowed that up and any opinion to the contrary was silenced. Here we are hundreds of thousands of lives and hundreds of billions of dollars later...