Quorn have made 'Crispy Nuggets'[1] from funghi for decades. They're a great replacement for chicken nuggets and I feel like if someone ate them without realising they wouldn't question what they're eating.
But I'm still of a mind that if you want to promote vegetarianism, make vegetable recipes taste better; don't make the vegetables imitate something they're not.
You're suggesting it's activism when it's just making a product for vegetarians who still enjoy the taste of meet from time to time.
For instance, some of these replacement items can't be boiled as one might in making a soup. It makes it difficult to complete a meal without refactoring the whole thing in some cases.
Plain meat is pretty... From what I recall typically doesn't have much taste without several additives like salt, butter, herbs typically marinated... You can do all that with the replacements, typically.