这句话有语法错误吗,有的话怎么改,没有的话help那里怎么解释

But others,on the contrary,insist that [offering aids to strangers/helping strangers] is not only [an act] out of moral principle.but also [a way] to show their humanity.
...补了下字~
1.people help strangers 改成名词 offering help/helping
2.补上宾语 an act
3.增a way 使句子对偶

有错误。help和is是同一个分句里出现了两个谓语动词，我认为仅仅把help改成helping还不能解决全部问题（people和is的搭配也有问题）。要改成地道一些的句子，最好更改两处：
1、去掉is
2、在show前加to

有错。应该是
But others,on the contrary,insist that it not only is out of moral principle but also shows their humanity for people to help strangers .
---------在这里，最好使用 it 做形式主语的结构。

个人感觉没错，people help strangers 是后面的主语