Is it a problem if I just watch those movies online like other people?

You seem to be asking if you can watch movies that are online for free, even though you have reason to think those movies have been placed online in violation of copyright law. Is this what you are asking? I think using such websites is a mistake, because those sites tend to be loaded with malware and viruses. You may save a three dollar movie rental fee and destroy your whole computer. Also, the sites may be honeypots trying to catch people watching or downloading child pornography. These are really big risks you are taking. However, I am not aware of any law that makes it illegal to stream, as a viewer, material that violates copyright. If you download the movie, even temporarily, you are violating copyright. If the system you are using does that, you are in violation.