i did muay thai for 8 years and fought at amateur level. i have now been doing normal boxing for 3 years. i have also been working as a doorman for a few years. in a 'real world' situation karate, taekwondo, kung fu etc count for **** all. if you're with your missus in the pub and say 3 lads start kicking off and jump u at once then 90% of the time you ARE going to get battered. all the fancy kicks, punches, blocks and kata's that you learnt in your nice warm dojo go zooming out of that pub door along with your ego and courage once you are bleeding on the floor. the thing is karate at the end of the day is a 'show' martial art. the training is regimented and doesn't prepare the body or the mind for punishment or real contact. i will get in the ring/street with any practioner of karate no matter what standard and would fully expect to beat him with in 2 rounds. muay thai doesn't just train you to kick and punch - it also trains you to grapple and fight dirty using knees and elbows. and through the training your body gets conditioned and learns how to accept and take damage. theres nothing fancy about it. its a brutal martial art (martial art - rubbish term) that has served me very well in my line of work and has protected me when i needed it to.
go along to a class - you don't have to do the fighting, just do the training - you will end seriously healthy!