The Thaksin government used its position to fill all of the check and balance institutions with its proxies, or to literally buy off those who were not direct proxies. These institutions included famously the extremely powerful election commision whose job became basically to insure Thai Rak Thai (TRT) electoral victories by holding elections in a manner that would favor the ruling party and by insuring no complaint against the ruling party would be upheld. One of their most interesting rulings was that if state money were used to buy votes it was not deemed to be vote buying. Vote buying has been rife in Thailand. Another of the check and balance institutions undermined was the supposedly non-partisan Senate. A block vote was basically bought. The auditor-general spent most of her term fighting to keep her position after the senate claimed she had been improperly selected. She was not able to do her job. She was not a Thaksin loyalist. The National Counter Corruption Commision that was supposed to check on corruption was never even selected as the government and Senate tied the selection process into a legal knot. While this was happening every complaint of corruption was reffered to this body. There is now a backlog of over 10,000 cases.
The government strictly controlled the state media rarely allowing a critical voice onto it, and newspapers faced having all of their advertising pulled if they allowed criticism.
The alienation of the Muslims in the South from any complaint proicedure has surely fired the flames of insurgency too. The disappearance of human rights lawyer Somchai who was chairman of the Muslim lawyers association remains a very dark mark over the Thaksin government. Thousands of deaths in the so-called war on drugs were not even investigated.
The TRT politcally interferred with the national police force, so that they enforced the politcal agenda of the ruling party and ignored any public complaints against the ruling party. This was particularly severe when opponents of the regime (and it was a regime at the end)started street demonstrations. The organisers always managed to keep these peaceful on their side. However, the response they met was not always so. Buses bringing demonstrators to Bangkok were routinely delayed and sent home. Some of the early smaller demonstrations were attacked by forest rangers organised by the natural resources minister. Complaints led to no action. Later a national newspaper was surrounded by a drunken mob organised by the PMs office minister. They threatened to rape any woman in the building. A similar mob tried to attack another newspaper office but local residents actually repulsed them. Then the opposition Democrat party who had nothing to do with the rallies held a meeting in the Northern town of Chiang Mai. The police stood aside as another gang of forest rangers attacked the meeting and  an ex-PM was assaulted. Again complaints were ignored. Similar attacks on opponents of the PM continued around the country. When shoppers booed the PM they were assaulted and an old man was kicked repeatedly on the ground and a five-year old child beaten. The police were filmed standing and doing nothing. Complaints were made but the response was any demonstrator against the government would be arrested if they caused people to attack them! Throughout this series of demonstrations General Sonthi refused to get inolved in a state of emergency when pressed by the government. The Thai military was just about the last institution that had not been packed with proxies although there were enough Thaksin supporters commanding units in Bangkok, and the exact mechanics of the coup are interesting in themself., but that is another story.
There is a lot more including an alleged attempt to assisinate the PM with a bomb, which most believed was just a publicity stunt to divert the news cycle from his supporters increasing violent action. Some of this had seeped onto the normally pliant media.
It all ended with a huge street demonstration planned by the People's Alliance for Democracy for Wednesday 20 September against the PM. Of course the coup changed all of this. It is interesting that the PM had a well prepared state of emergency speech that he read some of from the UN on Thai TV. This combined with the discovery of armed forest rangers in Bangkok has led many to speculate that there was a TRT plan to attack the Wednesday demonstration and then declare a state of emergency. Maybe we will find out more on this in the coming weeks.
Anyway, what I have tried to do is try to give some kind of feel to the atmosphere that led up to the coup  that will hopefully explain why the coup has received such support in Thailand.