I don't mind helping to carry these things to your home.(besides),the walk will do me good.I don't mind helping to carry these things to your home.( besides),the walk will do me good.为什么不能用 instead（instead含“相反”之意）在句

I don't mind helping to carry these things to your home.(besides),the walk will do me good.I don't mind helping to carry these things to your home.( besides),the walk will do me good.为什么不能用 instead（instead含“相反”之意）在句
I don't mind helping to carry these things to your home.(besides),the walk will do me good.
I don't mind helping to carry these things to your home.( besides),the walk will do me good.为什么不能用 instead（instead含“相反”之意）在句中也可以说得通呀?

I don't mind helping to carry these things to your home.(besides),the walk will do me good.I don't mind helping to carry these things to your home.( besides),the walk will do me good.为什么不能用 instead（instead含“相反”之意）在句
在这里并不是要表达“相反”之意,不能用instead,而是要表达而且,另外的意思.
我不介意帮你拿这些东西,而且,步行对我也有益.

instead的意思是“除了……”，描写对象排除在外，而besides的意思是“除了……还有……”，描写对象包含在内。