The Chinese Communist Party certainly was worried that capitalism would pose a threat. Turns out the Party is doing just fine.
"capitalism", i.e., a market-based economy is flexible and can be harnessed to serve whatever purposes a society desires.
So, no capitalism is not a threat to democracy, or communism for that matter.
Let's not forgot that capitalism is a recent invention. Kings and emperors were imposing their rule on their poor subjects without the help of free market economies for most of human history.
Right wing resurgence is back because the parties of the left forgot who gave birth to them - the working class. "Working class" is anachronistic now. The children of the working class became middle class. The new working class is now the middle class, increasingly being hollowed out.
What's to stop authoritarianism:
1. remove proportional voting. Coaltions allow parties to divide up the electorate. On the other hand, forcing parties to win 50%+1 of the vote forces parties to take broad-based policies that appeal to wide swathes of the electorate.
2. Invest in a social safety net. Education, healthcare and affordable housing promote social mobility, and more importantly, give peace of mind to those in the middle class who are afraid of losing the gains made by their parents.
3. Campaign finance reform. Its easier to turn out the vote and raise funding when parties turn to identity politics because nothing is more personal - and fires one up more - than appeal to one's identity.
Identity politics is cancer on democracy. Both left and right play the game and identity politics should be banned in a liberal (the John Stuart Mill kind) democracy.
4. Ban targeted political advertising. A liberal democracy needs a shared public space, and a discussion among all voters. Targeted political advertising breaks up that public space into millions of shards. Another option could be to force parties to post publicly all political adverts for everyone to see.
I ought, indeed, need to know what a party's policies are regarding pensioners or education even though I am neither a pensioner nor have children. Why? Because my taxes will be funding such items.
5. The left needs to be remember its origins. Sounds simple eh?
6. Finally, we need to drop the left-right way of identifying policies. It reduces policies which impact people and society into a basic for/against divisive manner. There is a better way.
Enough for today :)