Are we close to gene editing where humans can detect diseases beforehand and get rid of them? If we are not what is holding us back?

Yes, retroviral gene therapy is in clinical trials, though I don't know if they're human or nonhuman trials. There's still a lot of testing to be done before it'll see any approval.

As for what is holding us back, there's ethical problems to consider. Certain diseases are obviously ones we'd want to get rid of, like Huntington's disease. However, would it be ethical to prevent autism? ADHD?

Ensuring that we don't wander into the realm of eugenics is really important.

If I was a parent I wouldn't want my kid to have cancer or something similar if I carried that gene. I would like for my kid not to have it so he or she can live long.
- Yes, but imagine it starts to transform into avoiding ADHD, and after some time avoiding gingers
And what about being gay or trans, or even modifying race-associated traits?

Ethics, mainly

In the case of embryo cloning, it's Sophie's Choice but for embryos. Make a few dozen combinations of sperm and egg, and then choose the best one to grow based on your opinion. But embryos are people too. How many potential sibs can you waste for the perfect child? It's icky, and we should have caution when we do powerful things.

Individual gene editing therapies are also being worked on now, but these pose similar issues.

What if taking away depression from the next few generations causes the human population to no longer produce quality artists? Another issue: the wealthy will have unequal access to it compared to others. We can only have nice things (freedom from disease) if there are those willing to ~~pay~~ charge for them. Not everyone can benefit from gene therapy, so it is not truly a benefit to society or humanity, and therefore should not be developed as a biotechnology. As if that ever stopped anyone.

But embryos are people too.

Eh, they're not people yet.

How many potential sibs can you waste for the perfect child?

Human bodies produce way more gametes than most people want children, so I'd say that one could "waste" quite a few.

Not everyone can benefit from gene therapy, so it is not truly a benefit to society or humanity, and therefore should not be developed

Strongly disagree. While socioeconomic inequality is an important issue to address, that is no reason to halt scientific research and technological progress.

Assuming corps don't crush it I think we are very close to gene therapy but it will come in many forms. Get your immune system to clear out bad things or get your cells to make correct proteins and im sure other things I can't think of at the moment.