There are many volunteer opportunities where you can be sure that people aren’t taking advantage of you. For example, I regularly volunteer to help people learn how to program computers so that they can enter the tech industry, especially focusing on people who are at risk of falling through cracks. I don’t feel any risk that people will take advantage of me, because I allot a certain amount of time for it, and I know where my boundaries are.
Even if someone were to take advantage of me, a person can’t expect to go through life without that happening at some point. You have to weigh the risks and benefits. It’s difficult to make advancements in life without taking some risks. It gets easier to gauge those risks with experience. Getting burned a few times is just the price of gaining a bit of street smartness. It’s only a tiny risk if you do things right, especially considering the benefits to your own health and social connections. I’d be more worried about being exploited by employers than by volunteer situations. In my own life, I’ve felt exploited by many employers but have never felt that way while volunteering.
Another example of how a person can volunteer without risk: homelessness is a big problem here in the San Francisco Bay Area because high tech salaries have increased the cost of living which has driven many locals into the streets. (The average price for a 1-bedroom apartment was something like $3,500/month last year, and minimum wage is $15/hour or $2,600/month with full-time hours.) I have some friends that volunteer to help feed homeless people. There is no risk of being taken advantage of, because they know in advance how much time and effort they are committing, and they get a lot out of it in return.
There are many opportunities like that out there. If you can find an issue that is important to you, there is probably some organization that deals with it that you can volunteer for.