in and of themselves可以翻成“它们自己本身”
It is dubious that these arguments in and of themselves prove that Marx is a utilitarian.意思应该是：这些证明马克思是功利主义者的论据自己本身就是可疑的.
小注：小生系工科学生,在校读研.英语水平有限,答案仅供提问者参考.小生不才,贻笑大方了^_^