I think the important thing is to use real olive oil, in other words the expensive stuff. Make sure it passes the fridge test (it should get slushy after four or five days in the fridge). Most mainstream OOs don't. I tried three or four, and none of them did. This could be a sign that mainstream cheap OOs are adulterated with cheaper veg oils, which I've heard claimed. A good OO should have a tangy smell, IMO, like cutting open a fruit very much unripened and I prefer oils that are already cloudy but they do have a much stronger flavor that can overpower things like mayo.
If you have to get the more expensive olive oil to feel safe, then it might be time to move up to the more paleo-ish friendly oils for mayo but I'm pretty comfortable with it if it passes the fridge test.
I think it's healthy enough. I eat it and my blood tests are great. Paying 10x more to extend your lifetime by 15 nanoseconds isn't worth the extra money IMO.
I've found that the light oil works very well for making truffle oil. EVOO is strong flavored stuff and masks the truffle odor. It makes a nice slush in the fridge, to spread on steamed chard or whitefish.
I've been using light olive oil for mayo also. I'm big into "choosing your battles" and my initial thought was "well, it's definitely better than commercial mayo" but with all that's been coming out about olive oil lately, I don't know. I think I'm going to switch to half light olive oil, half macadamia or avocado oil; I'm not going to break the bank over my mayo, but I'd like to improve the healthfulness of it.
Light and mild olive oil is a highly refined oil that producers extract via industiral means (i.e., it is not the cold expeller pressed method favored by paleo folks for minimizing damage to the oil).
If you don't care for the flavor of regular olive oil, I'd suggest making your mayo with macadamia nut oil. It's a pricy oil, but might balance out since mayo is a condiment. And macadamia nut oil has a great fatty acid profile.
The problem with light olive oil is that it might not be olive oil at all. The book Extra Virginity documents widespread fraud among olive oil bottlers. A significant portion of extra virgin olive oil sold in American grocery stores is definitely not extra virgin and and some of it is highly processed seed oils. Light oil is farther down the food chain from extra virgin and more likely to be less than promised. I've been using "light olive oil" to make mayonnaise too, but am going to experiment with other options now that I know there are serious questions about what is in bottles labeled light olive oil.