Did you ignore every word Mace said?
"In the name of the Galactic Senate of the Republic, you are under arrest, Chansellor".
"You are under arrest, my lord"
And the lightsaber is not the weapon of the jedi, it's their tool. Mace was informed that Palpatine was a sith lord, and the intentions of a lightsaber is not to kill. Him igniting it is for security purpous, not attack.....
Giving everyone the right to do whatever they wanted would **** up the world. People would go around killing eachother and before anyone could say stop, everyone would be dead. There are limits....
Have you ever watched shows like "Cops" or something, where they film cops in action? They force people into their cars then drive them down to the station, against the thiefs will. Did they do anything wrong? No, they did their job, as do the jedi. Obi-Wan made a weak-minded fool a favour by ENSURING he would get a better life. Why let him ruin himself and continue to do illegal business (which the jedi would stop him from doing, or any other police of that kind) when he can simply give him a better life....