The very word "capitalism" immediately gives people the mental image of fat corporate magnates in old-fashioned suits smoking a cigar (bonus points for an old-fashioned monocle), running huge megacorporations that exploit poor third-world countries, exploit consumers, tear forests down and pollute like there is no tomorrow.
The thing is, what people, especially the social justice warriors, oppose is not capitalism, but corporatism. Uncontrolled capitalism can lead to corporatism, but they are in no way synonymous.
Capitalism is defined by the dictionary as:
The core feature of capitalism is who owns and runs the corporations: The government, or private individuals and entities. It's essentially a question of ownership.
The vast majority of the world uses a capitalistic economic system. While the government regulates what corporations are allowed to do (in an optimal system to stop corporations from abusing their powers and exploiting people), the corporations are nevertheless privately owned, not government-owned. The government does not own the corporations nor their wealth; it simply regulates their activities to ensure fair non-exploitative behavior that optimally benefits everybody (ie. the citizens, the government and, ultimately, the corporations themselves.)
Corporatism, however, happens when the government is unable or unwilling to control and restrict corporations strongly enough, and they are allowed too much leeway, which in turn almost inevitably leads to corporations abusing their powers and exploiting people and the system. Corporatism is, essentially, these private corporations being allowed too much power and too much control, often even control over the government itself. When private corporations have too much influence on the government (rather than the other way around), that's when things can get ugly. That's when the system has become corporatist.
This is what people, including SJWs, oppose. The vast majority of them just don't understand it, and instead just think it's "capitalism", and throw the baby out with the bathwater, so to speak.