No, it's not at all. The main complaint about Safe Spaces is that they are irreflective of the Real World®, and in the Real World® people will challenge you and this challenge is useful to help you grow and develop as a person.
However, a Safe Space is useful if is it not defined as somewhere which represents the challenges of the Real World® but which is just separate from them. A place where one can guarantee one won't be judged or criticised. It's a place to be able to speak up and speak freely without negativity or recrimination.
Even at work we have a Wellbeing Room - does this mean that the Real World® has comfy chairs everywhere, bouncy squishy stress-balls and colouring books around every corner? No, but we can create places which make us feel good so we can avoid, and recover from, a lot of the horrors out there.
As you've pointed out, this can be therapeutic and the main reason why a lot of people won't tell others what they're feeling, as in 90% of the time, is because they're scared of the reactions they'll get. If one can guarantee there will no negative reactions, such places can go towards improving the mental health of people.
Another reason why there is such wild dissent to such things is because it challenges the status quo. If things have been like X for a long time, Y is inherently thrown out, but most of the time it's just the change itself that people reject, rather than what is changing. The irony is that things have to change in order to develop: if they don't develop, they risk irrelevance.
Yes, I started this thread ironically but, given some of the responses here, I would support one on OCUK because this place can be toxic at times. This thread could even be a place to thrash out the concept before one is created at a later date.