In the forum I see many big scammers continue their work, their accounts only have red tags, on the other hand, I see many accounts getting banned for plagiarism.
So my question is now is the crime of plagiarism more offensive than scamming?

The both are offensive, if Plagiarism should be tolerated whereby users won't be be banned, it will kill the forum and make members to be lazy, the forum will no longer have standard. Scammers giving red tag can always be avoided by forum users, you can kill all the thrives in the world because they are bad to the society.