Tom Steyer entered the Democratic primary with a singular advantage: the largest fortune of any 2020 candidate. It could also be his biggest liability.

Reflecting on the ethics of a billionaire candidate at a time when growing inequality is a key election issue, the former hedge fund manager and Democratic party mega-donor offered up an unusual defense: Queen Bey.

“Should we put a limit on what Beyoncé makes? I don’t see why,” Steyer told the Guardian by phone. “I don’t think in the United States of America, we should put a ceiling on how far people can go.”

Steyer transitioned to a critique of communism and the argument that “at the heart of every great fortune is a crime”: “What Karl Marx failed to take into consideration was software – that if you are Michael Jackson or Rihanna or Beyoncé or anyone producing an idea, with software you aren’t just the best singer in your village … you have an ability to reproduce that song infinitely at very low cost around the world.”

Steyer announced his surprise campaign last week, six months after he publicly declared he would not be running. The 62-year-old Californian is now tasked with distinguishing himself from the other white men with no widespread name recognition in the 2020 field, convincing voters that he has long been using his money for good – and that the best way for him to help save the planet is from the Oval Office.

A longtime San Francisco resident and father of four, Steyer founded the hedge fund Farallon Capital Management in 1986 and left in 2012. Worth an estimated $1.6bn, he has spent his money advocating for clean-air and clean energy laws, opposing corporate tax loopholes, taking on tobacco companies, registering youth voters and other liberal causes.

Over the past year, he got attention traveling the country with his group Need to Impeach, which garnered more than 8 million supporters who want to oust Trump from office. The impeachment advocacy has earned him a Twitter insult from the president (“Wacky & totally unhinged”) as well as shade from some fellow Democrats. Steyer’s other not-for-profit group, NextGen America, has spent millions rallying people around the climate crisis and registering voters.

Steyer has pledged to spend $100m on his 2020 bid – more than the combined fundraising of the five highest-polling Democrats in the last three months. The billionaire almost immediately faced backlash and skepticism from progressive activists, some begging him to spend the money on something else, such as down-ballot races and voter registration.

“Democrats are expressing frustration that he is going this route rather than putting $100m into trying to flip the Senate,” said RL Miller, the chair of the California Democratic party’s environmental caucus, adding that her immediate reaction to Steyer 2020 was “eye-roll emoji”.

The US senator Elizabeth Warren has already solidified herself as the leading 2020 contender calling for impeachment while the Washington governor, Jay Inslee, has become the definitive climate crisis candidate, Miller said: “I’m not sure what [Steyer] can add? The ‘business man with no prior elected experience’ lane?”

In an interview on his way to the airport after a campaign stop in South Carolina, Steyer explained why he decided to run after declaring in January that he would spend “100%” of his “time and effort” in 2019 on impeachment.

“Part of it was watching that failure of government and just being so frustrated,” he said. “Literally, watching the debates and watching this campaign evolve, I thought, ‘Wow, I can’t sleep.’”

On impeachment, he said, “We’ve won the argument but we haven’t won the fight.”

Steyer’s bid has drawn comparisons to billionaire ex-Starbucks CEO Howard Schultz, whose flirtation with a White House run was derided as a wasteful vanity project.

Asked if anyone close to him had discouraged him from running, Steyer responded, “No.” After a pause, he said, “I’m not teasing!” He also said he knew that running wasn’t necessarily a “smart move”, adding, “I’m not trying to do a smart thing, I’m trying to do the right thing.”

Asked why voters should support him instead of Warren, who shares his views but has actual elected experience, he said, “I’ve been doing this from the outside for 10 years. She is a US senator in her second term.”

On the complaints that his money could have greater impact elsewhere, Steyer’s answer was simple: he’s got a lot of money. “We’re going to do everything we otherwise would’ve done,” he said, explaining that he was continue to fund NextGen and his impeachment group.

Entering so late in the race, Steyer already missed the first debates and is starting at a disadvantage. He may also struggle to convince voters that he would defeat the president – the question, polls show, that is most important to many Democrats, said Jessica Levinson, a Loyola law school professor. “That feels riskier when a person has no track record and is running as a business person who has made money in areas that I think go somewhat against his campaign narrative.”

Levinson was referring to his hedge fund’s past investments in private prisons and coalmining, a legacy ripe for attacks. On prisons, he said, “That was 17 years ago when there was no talk about any political stuff … It was wrong, and I ordered them sold.”

In terms of profiting from fossil fuels, he said, “We invested in every part of the economy.”

Outside of impeachment and climate, Steyer’s policy views are less known. On reparations, a subject of intense debate in DC this year as some Democrats have pushed for legislation, Steyer said he supported a bill to study it, but did not say whether he supported financial compensation for the descendants of slaves: “It’s not a question of whether this discrimination took place … and whether we should address it. The question is how best to do it.”

While some of the more left-leaning candidates support Medicare for All or a single-payer government system, Steyer noted that 150 million Americans currently have “employment-based” plans, adding, “They should be allowed to make that choice. We should not make it illegal for them to have that healthcare.”

Pressed on the ethics of billionaires in society, Steyer was quick to note that he and his wife have pledged to give away the bulk of their fortune in their lifetimes, and praised Senator Bernie Sanders and congresswoman Alexandria Ocasio-Cortez for pushing the notion that “inequality is absolutely a shame on America”.

“The idea of generational wealth is not one that I subscribe to or believe in,” he continued. “Should we have a different tax system? Absolutely. Should resources be shared differently? Absolutely.”

Steyer said his personal journey is one he would like to see America take, in terms of the move away from fossil fuels: “I realized that climate was a problem, I divested myself personally. I quit my job. I worked on climate hard for more than a decade.”

He added: “Do I wish that I figured it out sooner? Of course I do. But we all have to make that transition, and not to be a snot, but I think I was way ahead of almost everybody.”