(Note: Asking your "question" here is fine - it's about the site itself, and that's what the discussion tag is for.)
First of all: there is nothing inherently wrong about users with 1 rep. Everyone starts out there. All that having 1 reputation point means is that you're a new user. Fact, not judgement.
Secondly: you have no way of knowing, as a fellow user, whether those 1 rep users are secondary accounts of existing users, or if they are people who discover the site for the first time.
We don't actively encourage people to create multiple accounts on the same site, but as ChrisF mentioned, sometimes people want to ask questions with more anonymity than their usual account affords them. That's fine. Secondary accounts are problematic if they're used to engage in fraudulent voting, but we have staff and tools in place to catch those instances.
I would like to gently encourage you to reconsider your thinking that "To have only 1 rep people asking questions is not serious". Stack Overflow is still growing - rapidly. We acquire a lot of new users. These users all have to ask their first question and start off at one account; we require that users on SO register before they're allowed to post a question. Have faith that many of these 1-rep users are trying to get involved in the community.
That being said, there are still tens of thousands of higher-rep users active on here. It doesn't seem like the site is being overrun by new users. Only 14 out of the 50 most recently asked questions on SO when I just looked were asked by 1-rep users. And as I said before, you shouldn't automatically discount questions by new users and refuse to answer them; some of those might not be ideal for SO until the users learn more about our model and more about our rules, but you don't know until you read them.
Some new users don't stick around - that's okay. If a user only asks one question and leaves, that doesn't mean they've wasted anybody's time. What if that one question they asked is then viewed by 1000 other people with the same question? I'd say that was a pretty valuable contribution to the site.