I too have read that a vegan diet is good for preventing diabetes and therefore vegans are less likely to develop diabetes, but even if that is true the science is presumably more relevant to non diabetics. A study that looked at the long term effects of a vegan diet for diabetics would obviously be more useful to us here as we are a diabetic forum first and foremost. I don't know if there is such a study, maybe too early for one as of yet, but I would be genuinely interested in reading it.
My personal opinion echoes what many others have said. Vegan can be healthy, unhealthy, low carb, high and lots of other things too. Likewise, a meat based diet can be healthy, unhealthy, low carb, high carb and lots of other things too.
I personally think human health and nutrition is a lot more complicated than just meat or no meat.
In reality there are many other factors which influence people's diets as well as health. The people you live with, the place/community/country/climate you live in. Culture, ethics, religion, wealth, poverty not to mention personal tastes.
In the end people will eat what they want to eat regardless of what science says. If someone wants to be vegan they will be vegan. If someone wants to eat animal products then they will eat animal products. I suspect this will probably always be the case and the only way to be truly happy in this world and not let it upset you too much is to simply accept that.