I still eat both & don't worry about it. I look more at ingredients in a product. Butter is made from heavy cream & nothing else unless you add a bit of salt.
I stopped looking at the mayo ingredients list. There are some preservatives in some brands their that don't need to be IMO. I really should make my own from scratch & have no excuse not to. It's not that hard to do.
The original Hellmanns was made from eggs, oil, vinegar & seasonings. Now the label lists whole egg, egg yolks oil, vinegar, salt, natural seasonings, sugar, lemon juice, water & Calcium Disodium Ethylenediaminetetraacetic (EDTA). According to one article the last ingredient, a chemical preservative, has caused Hellmann's not to be sold at Whole Foods. Since I don't shop there, I don't know if that is accurate.
If you ever want to make a grilled cheese, use mayo on the bread instead of butter. It works out great, especially if your butter isn't soft enough to spread without tearing your bread up.
If you haven't tried Japanese mayo, try it. I've found the Kewpie brand at a specialty store which is good, but now both Walmart & Meijer are carrying it. At Walmart it was in the oriental/international food section & not with the other mayo. Kewpie's ingredients are vegetable oil (canola/soybean), egg yolk, vinegar, salt, MSG, spice & natural flavor.