If you want to make the point that killing those illnesses with soap is going to keep you safer, go ahead.
But to say it will "help maintain a strong immune system" is incorrect. It may protect you from viruses, bacteria, etc. but there is no medical evidence to my knowledge supporting that your actual "immune system" will get stronger as a result of using soap.
To say that the immune system will have an easier time functioning may be correct.
I have also heard that too much obsessive hand washing will make you too germ free, and thus your immune system will get used to not having much work to do, the same way your arms would get flabby if you never lifted anything. All the muscles, nerves, etc. in the body must be used occasionally to promote good health, and this undoubtedly includes the immune system.
I've even heard that a lot of illnesses were more easily beatable 100 years ago when our immune systems were stronger because we weren't trying to live in a sterile world. But I'm not saying you have to roll around in the mud with pigs or anything, I'm just saying don't try too hard.
And always be sanitary in the cases where it counts the most or if someone around you is sick.