So I'm not overly familiar, but I can try to summarize what I know.
Steven van de Velde is a Dutchman who went to the UK and raped a 12 year-old. He was sentenced to four years in prison for this by a UK court. Later he was extradited to the Netherlands, so he could sit out his sentence in the NL. However in the Netherlands, unlike the UK, sex with a minor is not automatically considered rape and needs to be proven in court. (Note: That is my understanding of the difference in interpretation) Because of this his conviction was reduced to "ontucht", meaning sexual misconduct. (Even though what he did would probably also be considered rape in Dutch court).
As a result, he was out of prison after 13 months.
Now, Dutch attitude to these kinds of things, in my experience, is generally (but not always) that if you have paid your time, and have shown remorse for your actions, then it should probably not affect your future career prospects. The justice system is supposed to rehabilitate after all. (That is my experience though, and my experience may be biased, so don't take this as gospel)
Hart van Nederland did a survey, and apparently only 27% of respondents think he should not be allowed to compete. 63% of respondents think he should be allowed to compete, and 10% don't have an opinion either way. (Note that Hart van Nederland is not the most reliable of sources, but it gives an indication)
From what I have seen in Dutch circles this controversy is a lot less pronounced than it is in other countries. That's not to say it is entirely uncontroversial, but it's not quite to the same degree as I'm seeing internationally.
Personal opinion:
I don't think his sentence should have been lowered to "ontucht". I think what he did is morally reprehensible, and he should have sat out the full sentence for raping a minor. That is a failure on behalf of the justice system though, and van de Velde is not personally to blame for that.
That said, given that he has shown remorse for his actions, and has finished the sentence that the legal system imposed on him, I don't think he should have been barred from competing in the Olympics on behalf of the Dutch team.
Edit: As Flying Squid mentioned I might be mistaken that he has shown genuine remorse.
If he hasn't that changes my opinion on the matter.