What is it that Biden supporters believe they will gain?

I dont want to gain anything, I just want Trump gone

Biden supporters have been brain washed into everything.  They have NO idea who pays for 'free'.

Biden supporters believe they will gain a return to the traditional American values of liberty, democracy, honesty, the concept no one is above the law, and human decency.  In other words, everything Trump and his most ardent supporters are opposed to.  

You and I (an accountant) know that, but sheeple are easily swayed when you wave carrot$ in front of them.

Gain:  Peace, love and eternal cosmic wisdom.

Lose: Hatred, strife and a fat phallic cheeto.

$15 an hour is $600 a week (assuming 40 hours).  I don't buy $120 gallons of gas a week and I don't think many Americans do.  Double in sales tax and $5 a gallon for gas isn't as much of a problem is you're making enough to afford it -- and $15 an hour is enough to pay for the gas and tax and have a lot left over for other things.

There will be more jobs with open borders, because fewer companies will have to leave the country in search of the workers they need.  Many companies can't hire only Americans without also hiring foreigners, so the shortage of immigrants keeps them from hiring Americans either.  Open borders would allow them to hire enough foreigners to be able to hire Americans as well.  Closed borders force employers to move to other countries that have the workers they need, or to close down, so their American workers lose their jobs.

"double in sales tax"

Double of zero federal sales tax is zero.  

FTFY.