They do not allow you to take poles into the cabin they must be checked.
I think it’s important to specify which country of departure we are talking about, and who the “they” is. As Annie and others have said, folded up poles are almost always allowed to go through US TSA security. The airlines are usually not involved in that decision, at least not in the US.
Going through security in Spain is a totally different matter. You cannot carry them on in Santiago under any circumstances.
If you check in in Madrid, either as a transit passenger going from US - Madrid - Pamplona (Valencia, Barcelona, Almería, etc etc) or on your way home to the US, you are also unlikely to be able to carry them on. This presents a problem for people who carry on their poles from the US and arrive in Madrid to change to a different flight, only to discover that they cannot take them on the flight. As a transit passenger, checking your poles means leaving the secure airport, standing in the check-in line, checking the poles, and then going through security again. This could be a long process that means you miss your connection.
So here’s what I would recommend for US forum members.
1. If you are flying US to Madrid, fold them up and put them in your pack and carry them on. But have a Plan B way to check them if TSA says you can’t bring them on. I would never ever check my pack, even though, as others have pointed out, the rate of lost luggage has decreased a lot. But just ask Annie Santiago about how much fun it is when a pack does get lost.
2. If you are flying US to Madrid to another city in Spain, check the poles in the US, carry on the pack, and hope the poles arrive.
3. On the way home, check the poles.