How to do an if-else comparison on enums with arguments

Language: Swift2.3

For example let's I'll show you different kinds of enums

enum Normal {
    case one
    case two, three
}

enum NormalRaw: Int {
    case one
    case two, three
}

enum NormalArg {
    case one(Int)
    case two, three
}   

Switch can be used on all three enums like so:

var normal: Normal = .one
var normalRaw: NormalRaw = .one
var normalArg: NormalArg = .one(1)

switch normal {
    case .one: print("1")
    default: break
}

switch normalRaw {
    case .one: print(normalRaw.rawValue)
    default: break
}

switch normalArg {
    case .one(let value): print(value)
    default: break
}

On the if-else statement though I can only do comparison for Normal and NormalRaw, and an error message shows for NormalArg, so I can't run the code

Binary Operator '==' cannot be applied to operands of type NormalArg and _

Here's the code example:

if normal == .two { // no issue
    .. do something
}

if normalRaw == .two { // no issue
    .. do something
}

if normalArg == .two { // error here (the above message)
    .. do something
}

if normalArg == .one(_) { // error here (the above message)
    .. do something
}

if normalArg == .three { // error here (the above message)
    .. do something
}

Any Ideas? I'm not really doing anything with this code, I'm just wondering as to why we can't do comparison.