I dont know what gauge steel they are using for the border fence but it has to be 1/4 inch or better plate. It's likely thicker than that. You arent cuting through that quickly with an angle grinder. It's possible to cut through it but it wont be a 10 minute operation. That said fences are never intended to be a full proof way of keeping people in or out. They are a deterrent. That some people can come up with ways to get over, around, under or through a barrier does not negate the necessity of the barrier. You would agree that it's far easier to get over, around, under or through a barrier that doesn't exist vs one that does right? We cant hire or afford enough border patrol agents to patrol or monitor that large a border 24/7. The barrier presents a delay and one of many layers we do and should employ to keep people from illegally entering our country.