Muay thai and western boxing is a great foundation for self defence but you should always remember thay they are mostly praticed as a sport. I would recommend to also look at some disciplines like kali or escrima for some basic techniques using knives and other weapons if its self defence you are after. And dont fall for any fancy defence technics, just keep it basic and incorporate it in to your boxing or muay thai work. For example can you still throw a kick or punch if someone pulls a knife or should you just run etc. As a sport however Muay Thai is great! I have been training Muay Thai and western boxing for the past 10 years and will probably never quit.