Although I agree much of the Vit C we buy these days is synthesised as opposed to extracted...
If you don't like the idea of one kind of simple food molecules being turned into another simple food molecule by heat and bleaching (by simple predictable reagents used for centuries) and low toxicity, low mobility catalysts (that by definition aren't present in the end product) then you should be 100x more worried by what they put in every kind of processed food - even dried fruit. Not to mention complex and unpredictable pesticides, herbicides, fungicides.
I do worry about the complex synthetic stuff in our foods - that's why I grow my own and minimise the rest.
Home grown VitC in home-grown blackcurrant juice works just as well and the end result tastes better than the sum of its parts.
But to really worry about such simple stuff as VitC synthesis going wrong - that way lies the padded cell.
You need to apply the venerable and common-sense 'peanut test' - anything that's less deadly than choking on a peanut isn't worth bothering about. It covers 90% of what the newspapers would like to spook us with (including rail travel) and 99% of what alternative therapists warn us to avoid.
In fact it covers just about everything except what makes really big bucks for unscrupulous businesses.
