I can already tell I won't like you. On the list you go.

Just read some interesting threads and you didn't know you arlready posted more than 5 posts.

Well, the point it kind of the opposite. How do you control a decentralised inflation?
Cryptocoin is successful for the reason that it is not controlled by a single entity and therefore safer for your funds.
Of course bitcoin is infinitely divisible so instead of making more money, you split it into smaller pieces.
This has of course some negative consequences on the value of the coin since it will continue to grow after demand.

I have studied economics for years and I see no reason why inflating the currency is necessary.  Do you?

The OP title is fallacious. Login counts as an intensive database query (rightly so). The forum software limits repeat intensive database queries (which include searches) by enforcing a reasonable interval between queries. This results in a better user experience for every single user of the site. Ultimately, this means the enforced interval must expire between logging in and initiating a search (which is only what, 20 seconds?). If that is too big of an issue for you consider quitting the internet.

Use the 'Google Search' button you see after you click on the magnifying glass icon to the left of the search box.

In that vein, I think another reason for the 5-post count is to gently change the newbie mindset:

from something like "I've got to make five stupid posts when all I want to do is make a really important post as soon as I'm out of this stupid prison. What a dumb place this is that I really really want to join. They're obviously a bunch of idiots and I demand my right to join them right now or I'll hold my breath and turn blue..."

to something like "I can't think of anything useful to say right now, so I'll go and do some reading and when I have something interesting to say I'll say it and perhaps if readers find my post interesting we'll engage in conversation about it and I'll learn some stuff and... hey, I just noticed I've got more than five posts already so I'd better start to think seriously about how I can contribute to the other discussions that I'll be getting access to."

The present system isn't foolproof but it's better than many fora have. Lotta noise on the Interwebz.

Still don't get it?... Many people earn permanent "ignore" status before they even get out of the newbie quarantine zone.

For others, the "ignore" button gets pushed later, after they try a few troll posts and readers give them the benefit of a small doubt by looking up their post history.

If you post worthless posts, you will be treated as a worthless poster sooner or later, after which you just post into a vacuum. Not a bad system, all in all.

Post away!