Can't basic and heavy weapons be fired in close combat? I read that pistols can be fired in close combat. For me the converse argument is that basic weapons can't be fired. Am i right?

Yes, you are right.

• Pistols may be used in CC, even if two handed (like the hand cannons).
• Basic and heavy weapons may not be used in melee, even if one handed (for example by using recoil gloves).

Of course you can use them as clubs and, if a mono or power blade is attached to the basic weapon it may be used as a very effective spear.

Close combat is a great time to whip out the Ripper Pistol and make everyone cry!

That is why there are combat blades/bayonet attachments for basic weapons (and some weapons come with them). You cannot use them to shoot when in melee, so you use it as a mono spear/sword/etc rather than needing to drop the weapon and pull out a melee weapon.