I’m not sure that you’ve considered this fully??
Firstly he’s been in politics for many years so is bound to have at time voted for controversial things as he had to vote as a senator along party lines. For everything he has voted for throughout his career have you analysed what the oposite outcome would have been to the votes he made. The weird system in america for making laws means you could have a law to give every citizen a fluffy kitten but someone will have tagged on to that law some thing which saw every citizen gets a poke in the eye. If you don’t vote for the poke in the eye no one gets a kitten and so many of the laws are created like this if you don’t concede one thing then you throw out any opportunity to make a difference, you can’t just choose to not agree to one part or another, it’s all or nothing. Also he has a history he’s been in politics for years and knows how to get things done, is friends with many people from both parties. Trump doesn’t have any experience in politics and look what that’s achieved.... sweet fa, a 4 year period of throwing tantrums to try and get what he wants and what he wants is usually the poke in the eye.
On the point about same sex marriage Biden has been in favour of that and a staunch supporter of same sex marriage for years.
Anyway however you look at it all politics is “picking the best of a bad bunch” people get to become leaders and politicians often not by qualifications but by which party they represent, the voting habits of the areas they live in, the people they know and suck up to within their own party and how they play along once they have there seat.
People in the uk don’t usually vote for the policies of the candidate for there local MP but the views that there party represents even now the huge majority of people decide they are Labour, Conservatives or Liberal Democrat’s and the party that gets the most MPs in Parliament is the party that appoints their own internally selected leader as the next prime minister.
People often see the general election has picking the next prime minister but in truth on a general election no one is voting for the prime minister just the local candidate who if you favour and vote thinking you want Boris Johnson as the next prime minister then you’lo vote for your local conservative candidate who may well be the person in favour of giving everyone a poke in the eye, the alternative maybe a Labour candidate who’s borderline communist, not that it matters as very few people look at the actual person they are voting for or what there track record is. You want BoJO you vote for the candidate that gets you BoJo. At least in america people do vote for the president they want, which also sadly means you get people like trump who can buy there way in, you can’t buy your way to the top of politics in the uk, not like you can in the states