A semantic stopsign essentially says: "Okay, that's enough thinking, you can stop here". It's a non-answer disguised as an answer, with a purpose to stop you from asking further questions and revealing the truth.
Imagine your friend claims you should rub mud on your face before heading outside, as it will protect your skin from the sun and keep it hydrated.
"Mud? Are you crazy? Why would I do that?"
"It's recommended by scientists."
"Oh... well in that case."
That's a semantic stopsign. It's not actually giving you an answer for why you should rub mud on your face, rather the purpose is to stop you from asking more questions.
Learn to recognize these stopsigns and disobey them. Often the reason someone presents you with a semantic stopsign is because there's an uncomfortable truth close by. When a politician is asked a tough question and they answer "to defend democracy" or "to fight terrorism", they aren't really giving you an answer - they are saying "okay, that's enough questions, you can stop here".
When someone hits you with a stopsign, your natural reaction is to obey and move on. Next time, do the opposite and see where that leads.