It is illegal to target civilians. And both sides have been doing it. Both sides are wrong, and both sides are committing war crimes and violating international law and the Geneva Conventions when they do it. However, the government of the US and some other countries are only sanctioning Hamas for targeting civilians, while they assist the government of Israel in targeting civilians.

The people who use Hamas' behavior to justify the government of Israel's violations of international law and the Geneva Conventions are no better than Hamas themselves.