I read somewhere that Marc included the Cutlass in CT because US Marines still used the antiquated bayonet in the 70's, when Marc was writing Traveller.
My personal handwave has been that blade weapons are still relevant when you're out on the hull of a spacecraft fighting pirates. Cutting a life support tube is easier than shooting an enemy then dealing with the recoil.
So, when your accelerator rifle runs out of ammo, you pull the cutlass and REPEL ALL BOARDERS!
That's why one uses laser rifles in Z-gee... Also, it would take one incident before they decided to upgrade umbilical cords from cardboard tubing to something that can't be cut by a primitive blade weapon. Also, do you realize what happens in Z-G when you swing that sword? MUCH worse that the recoil from a firearm.
Good comments, HG_B. Food for thought.
I was thinking about the above exchange, and although HG_B makes some excellent points, I was also thinking about real life.
In a perfect universe the "cuttables" would be upgraded to something that couldn't be cut by blade weapons, as HG_B says. But, the universe isn't perfect, is it?
This is "us against them" thinking, as if it's our one army against their one army. But, out in the Empire, there are 10,000 worlds and probably as much variation on vacc suit design.
In a perfect universe the upgrades would be made if it were a very inexpensive and easy process. But, I don't think that would be true of a material that cannot be cut by blades, especially at the lower space tech levels. And, if the materials aren't available, or the cost is just too high, then even the higher tech level suits from manufacturers of certain worlds would not be protected either.
Sure, there are some upgrades with uncuttables--some premium suits from some planets. Maybe the Imperial Marine suits are made that way. But, the local Marines from the planet Boo-Boo may not enjoy the same quality.
On top of this, we haven't even started talking about Alien design and materials.
Therefore, I still go with my initial statement. The Marine cutlasses have a practical use for a Z-G Combat trained Marine, and that is to cut up the hoses and lines on an enemy's vacc suit.