Ok, I feel I need to make this clear:
-I'm not a USA citizen.
-I don't like Hillary.
-I don't like Trump either.
-If I was an USA citizen AND a registered Democrat, I'd have voted for Bernie Sanders.
-I agree that it was a retarded move to nominate a candidate under federal investigation.
Now, onto the point. Even if she was under a federal investigation, she had not been convicted. While I am not american, I believe an important saying in the justice system is "innocent until proven guilty". Now, I believe Hillary was guilty. But I'm not a judge or jury and I may not have all the evidence they hold.
So, since Hillary has not been convicted, she's allowed to win the presidency. And people voted for her. I won't discuss their motive, since, again, I would not have voted for her if I was an american (or for Trump either). The fact remains that more people voted for her. And they lost. Because of the electoral colleges. So people protest.
Now, regarding violent protests, I will agree they are not a good idea to be heard. That being said, the communist regime fell in Romania, my country, due to a violent protest that turned into a revolution. Without that, we might still have been communist now. Our neighbor Moldova is still struggling to get out of that. So, my point here is that, in certain situations, violent protests can achieve results. But you must be willing to stake your life on it, something I doubt these protesters are doing now. In fact, i believe most (not all, but most) of those protesting violently now to the election of Trump are just asking for an excuse to... be violent.