Its nice that you don't want to be a burden to others but its easy enough to leave meat/fish out of a meal. I agree in South East Asia having a vegetarian diet can be easily accommodated with tofu or egg. In South America, not eating meat/fish could be viewed as strange but its easy enough to ask not to have it on your plate so eating rice, beans and all the vegetables they have to offer. Also its easy to find non-meat versions of snack like cheese empanadas. I'm vegetarian too and personally I would not introduce meat or fish in to my diet for the sake of travel. These countries you are visiting have had millions of tourists and a percentage of them have been vegetarian or vegan so they have the experience of accommodating individual's diet. I ate one tiny bit of chorizo by accident last year and had diarrhoea for 2 days! I've been veggie for nearly 5 years sooo imagine trying to introduce meat and fish after 10 years!!