Are you really, 100% honest with your spouse, as in "I think I might have watched too much porn" or "I just can't stand our child, I think he's ugly and spoilt, sometimes I wish we didn't have any", or "I really don't fancy you anymore, I'm thinking about having an affair"...?

I would assume most people are not that candid with their partners, but that's the sort of thing you can discuss with a therapist.

Not if you're having relationship issues with said wife/husband. Your spouse is biased. Sometimes you need an outside perspective. Close friends are also an option, but there are lots of folks out there who don't have somebody they can really open up to.

Your spouse is not your therapist. They're not detached. They're biased. They don't have training (unless they're a licensed therapist, in which case they are definitely not your therapist). You can't get useful advice from your spouse when you need help coping with your spouse's issues.

I'm not sure the qualification "medical grade" exists for therapy. You go if you feel like you need to go. You would see a psychiatrist for medicine-based solutions to your perceived or physical ailments.

Another aspect is that often times sensitive subjects involving the spouse come up that you have previously been unsuccessful in discussing with them, or you are simply uncomfortable discussing with them.

An easy comeback would be to say "you should be able to discuss anything with your spouse," but reality ain't that simple for everybody.

For lonely people, it's much easier to get a therapist than a spouse.

You can, but I for one wouldn't want to burden others too much.

Trying to have the sorts of long lasting introspective unidirectional conversations needed to really work through things with your partner will either fail or screw up your relationship or both.

Obviously people do. But it can be enormously good for a relationship to have an external, non-personal, context for that kind of work.

But who will make money on that?