You contested the claim that he was democratically elected. I don't see how this is relevant to that claim.
In any case, I don't see evidence that his former allies were against him. Congress wasn't his ally, and besides - as the text you quoted says - there was an election in between, so they weren't all the same people. His allies were the UP, and as far as I can tell, they still supported him.
Finally, losing support from your allies means nothing. That happen just five years ago in my Western European country, and it might happen again soon. It's an expected development in a country with a diverse polity.
Where vague accusations?
"destroyed essential elements of institutionality" and such.
The economic situation of Chile
Which might make him a bad President, but still a democratically-elected one, which was the point being argued.
> only reports of vague accusations.
Where vague accusations? The economic situation of Chile during his regime went from bad to worse and his directives were directly responsible for it (as proven countless times in countries where the same policies were adopted). Check out the wikipedia page on the economy of Chile during his years.