Reasonable arguments only exist on one side of the political aisle?
To see good on only one side of the aisle and only see wrong on the other side of the aisle requires bias. It requires us to look at the facts as a serious of items from which we must carefully select what reinforces our narrative and which truths we must discard. As a reasonable person, you must surely have noticed that bias exists in every corner of the political world, not only on the side you do not vote for.
So while there were certainly non-objectionable things said and done by Mr. Trump, here are just a few of the real things that people strongly object to:
In 2015 two Boston men beat a homeless Mexican immigrant and urinated on him while voicing their support for Trump. Mr. Trump's response was "I think that would be a shame. I will say, the people that are following me are very passionate. They love this country. They want this country to be great again. And they are very passionate." One sentence expressing disappointment followed by four sentences of PRAISE. After letting that linger in the air for a day, the next he issued an actual condemnation. This became a pattern whenever confronted with racism: an ambiguous condemnation mixed with elements of praise, followed the next day by a full condemnation. That is neither normal nor helpful behaviour, and it has inflamed a lot of people.
Before both of his presidential elections Mr. Trump declared that he would only accept the outcome if he won. He told his base that there were only two possibilities: either he would win, or the election would be rigged. Never before has any presidential candidate declared that it is illegitimate to elect someone else. And indeed now the country is in a position where bipartisan courts and even Republican election officials are not trusted by a large portion of Trump's support base.
You will recall Mr. Trump was recorded bragging about groping women without consent. His defence was that he was lying. So that leaves us with exactly two possibilities: either he assaulted women and then lied about it, or else he told a lie bragging about assaulting women. Either way, we're left with the fact that the man is a lying pervert. People soured of that in Bill Clinton, and more than a few people strongly object to it in Donald Trump as well. Others are fine with it, but you can understand why some people are not.
You may recall that Barack Obama cracked down on illegal immigration. (or you may not) One of his policies involved extreme situations where gangs were entering with children, and children would be separated from the adults while matters went through the court. (Melania has talked about this) The Trump administration expanded the program to generally separate children from their parents simply as a deterrence to families trying to enter the country illegally. This came despite people inside the administration warning that they did not have the resources to ensure the children would later be reunited with their parents. There are quite a few people who are upset by destroying families as a policy.
You will recall that Mr. Trump was found to be lying about hush money paid to a pornographic film star with whom he cheated on his third wife, who was his third wife for being a woman with whom he cheated on his second wife, with whom he cheated on his first wife. It really is not unreasonable for people to distrust a man who has never been faithful to anyone but himself. He has continued to lie on a daily basis, outstripping the dishonesty of the men who held office before him -- an impressive and determined feat for anyone following Bill Clinton.
Mr. Trump's unparalleled commitment to dishonesty does not sit well with some people. Others chose to believe no one else except him.