Putting clothes on a dog is only cruel if your dog hates doing it.
Lucky, most dogs respond positively to treats (It's all about the treats). Here are three easy steps that will persuade most dogs to genuinely enjoy clothing:
1) Be patient. Before you even put a single article of clothing on your dog, first present the clothes to your dog with a few treats stuffed in them. Keep your voice high pitched and positive. Once your dog finds and eats the treats, immediately put the clothes away. Repeat this process a few times. The idea is to get your dog excited about seeing the clothes.
2) Put the clothes on the dog. In the case of a shirt, start by rolling up the shirt towards the collar until you have a donut shape. Your dogs head goes through the opening. While getting the legs through the sleeves, be careful not to bend your dog's ankles the wrong way!
3) Before your dog even has the chance to inspect the clothing, IMMEDIATELY offer him/her a treat... then another treat... then another treat. NOW GO FOR A FUN WALK!!!
Take the clothes off right when you get home. This will enforce the idea that the clothing is an awesome treat reserved for special occasions!!!