a plant based diet can be a very sound idea for obesity and related issues, if undertaken under professional supervision (see a qualified dietician who is vegan-friendly- and do not go nuts on the fast release carbs- trust me, i’ve been vegetarian since i was 3, and eating as vegans do for going on 10 years- you can be a fat unhealthy vegan if you live on rice-icecream and mashed potatoes- and it’ll not help your adhd one bit! 
).
but i’m gonna chime in and say that in my opinion, there is no one magic fix for everything for everyone, nor one big all encompassing universal evil- a large amount of modern pharmacuticals are standardised extracts of plants and minerals, which all come with their own risks and benefits, and it’s just as easy – if not easier- to kill yourself with stuff you can buy in the healthfood store, as any other store- especially if you’re not properly informed and aware of what you’re doing (alas, there are little to no requirements legally or ethically, when it comes to being educated about supplements, etc, when you’re selling them).
there is always gonna be strongly held opinion, rapid changes in perspective and knowledge, hyperbole and misinformation, etc, all over the place, cos people are …well… people, so we really do need to look at stuff for ourselves, reflect on it, talk to each other, and then make our own decisions- and respect each others right to do the same- and to courteously agree to disagree, if and when we don’t find each other on exactly the same page. i’m 110% in support of that.