Because if you want to live in a harmonious society that provides opportunity for everyone, it’s best to not create a huge wealth/income gap.

You cannot provide opportunities if you charge more to those who has more. You're just transfering money from one rich to another, unequally.

Reframe that question: Why should poor people pay more because they’re not rich enough for the incentives?

OP is not saying rich people should pay more; He’s saying get rid of the tax incentives. Yes, they end up paying more, but then poor people are paying the same as the rich.

One of the problems is ambivalence. For many, PV is "nifty" but unnecessary- if I go to a fast food joint and I have a choice between a pretty good hamburger for 1/3 the price of a pretty good hamburger made from beef substitute, which do you think I'm gonna buy? But if I'm told that I can get the beef substitute version for just a few dollars more than the regular version because of a tax break, you can bet I'm far more willing to try it out.

"Rich" (which is a relative term anyway) people are, by and large, the same. Get rid of the incentive and you'll get rid of the progress that comes with it. Saying "oh take away the incentive because not everyone pays the same amount" is a great way to get people to stop investing in it at all. It's not like poor people are going to say "oh wow, the rich people won't get a tax break for investing in this, now I'll definitely invest!" right? So poor people still won't be able to invest and now rich people will have less of a reason to overcome their ambivalence. Shockingly enough, taking away incentives will deincentivize people. Who knew?

Poor people benefit when less energy is generated from fossil fuels.

That doesn't answer my question. Why someone has to paid more just because it has more money in the bank, what makes you morally superior to get better tax cuts just because you have less dollars in it?