Should I take my own padlock for the door of my room while travelling in Thailand?

You can, but I've never seen a door capable of using a padlock. If you are staying in very cheap backpacker type hotels, then security is an issue. Mainly due to the foreigners.

If you are a at bit of a nicer hotel, or one without many young backpackers, then you're in pretty good shape. Same as in any other developed country around the world.

Unless you are staying in cheap, backpacker rooms the room wont have anywhere to put a padlock. Padlocks are cheap enough to buy when here so no reason to bring one with you and even with a padlock on the door I wouldn't leave anything of value in there. Generally though it is very safe. I have travelled all over Thailand and never had any problem.

Thais, and other people have all the keys to pad locks anyway, so why lock it, just don't keep valuables in you room.

Still trolling I see...

The difference between priced for a hostel and a nicer/safer place is very very small(at least in Chiang Mai). Check out www.airbnb.com Real places in pretty much any country. Generally better prices for hostel/hotels.

When you padlock the door to your room, the house keeper cannot get in to clean. Also, if there is a problem in the room, like flooding because of faulty plumbing, they cannot access the room to fix it. (I am seeing it through the perspective of a hotel owner). Just don't leave valuables in the room, I hate to say but especially in places with a lot of backpackers.