Even if all the far-left parties only get 1% or 2%, if the moderate left arty doesn’t have a clean majority, they need the votes of those far left parties to form a government, and thus the far left parties can negotiate some stuff. It’s not useless to vote third party.
Sure, but they don’t know, people lie. If we put in a balance your feeling being hurt vs them being murdered and/or raped, I’d say that unfortunately it’s better for now for you to feel bad.