Semantic quibble:
"The KKK kills black people, and claims to be a christian organization. Does this mean that christians kill black people"? results in the logical answer "Yes" -- There ARE christians who kill black people, namely, the KKK.
The rhetorical question you were looking for is "Does that mean *all* christians kill black people?", which lacks sufficient data to answer. ;P
This of course, overlooks the value of stereotypes. Stereotypes are NOT intended to judge individuals; they are intended to provide coarse assessments of large groups of individuals. For instance, the stereotype "Christians are superstitious." It does not mean that ALL christians are superstitious (unless you use some very twisted axioms about what constitutes a superstition such that belief in a deity is a superstition), it means that more often than not, when you encounter a christian, they will hold at least one superstitious belief.
Stereotypes are useful constructs when applied to aggregates. This is basically how big data works in fact-- Big data finds downright silly stereotypes based on metrics collected, which are then used to gain marketing advantages. The fact that big data works proves that stereotypes are useful.
The argument was against the stereotypical SJW; Not individual SJWs.
In essence, a Social Justice Warrior (SJW) feels that there is something wrong with how society commutes justice, and seeks to remedy this. This is in direct contravention of people who like the status quo. The extension of this is that if the SJWs dont like a specific form of recreation, they will seek to prevent you engaging in that form of recreation, since they seek to prevent that form of recreation being undertaken. (Let's use a purposefully bombastic form, such as spectator cock fighting.) The statement Sergarr made: "You're not allowed to have fun in any way that's not accepted by SJW community." is true-- You can have fun any other way besides watching two chickens kill each other, as far as that group of SJWs is concerned. When extended to the stereotypical SJW, which represents the sum total of all "Injustices" the combined assemblage perceives, vast stretches of the "Possible entertainment activity space" are excluded. Because those activities are not accepted by the SJW community.