I have felt the same way and would love to hear other people's opinion. I am a stutterer with speech blocks and I have been trying to self-study Vietnamese to be able to communicate with some family. Vietnamese is a tonal language with a lot of glottal stops. The stops really aggravate my blocking. The tones are easy for me when I'm having a fluent day or hour but when I block I try so hard to get the words out that when I finally say the word the Native speaker has no idea what I said possibly because my stutter messes up the tones. I'd like to know if any stutterers have learned Mandarin, Vietnamese or another tonal language specifically?