I don't understand your point of view, to be honest. You as a gambler, should have on among your biggest interests (when comes to betting) the potential profit of the fact you can profit of your choices, otherwise, what would be the point on betting in favor of Biden and against Trump?
The market of betting is about making profits, actually, I am sure there are people out there in this market who does not like Trump as a person or leader and still they believe he has better chances than Biden, so they bet in his favor. Politics and betting should not get mixed between each other, because in the end of the day, we are here to profit from this political even, regardless on who is on the ballot.
If you are rather moved to support Biden, instead trying to get profit, then you should donate to his campaign of to his party, that is a more coherent way to show political support than betting.
Because even if he loses, the money you donated to the campaign helped him to try get as far as possible, on the other hand, If you bet for him and he loses, then you money just changes hands to someone who is likely opposing to your political views.