I give homeless people money behind my parents' backs. Is this going to be something you disagree with?
No, not necessarily. But why are you giving money behind your parents' backs?
I don't want to hear their sermon on how able-bodied people need to get a job.
Your parents mean well in taking a hard line. However, sometimes other people try their best but have a run of bad luck. It's good to have have empathy.
They don't know how to ask for help instead of living on the street.
Your parents are entitled to their opinions, but it's okay if you choose to give homeless people money. Just do what you think is right and ignore your parent's sermons. You have a mind of your own and you know how to use it wisely.