Not to disagree with the idea, but I would add that any such tax is at the discretion of the taxing body making it susceptible to difficulties like abuse or negligence. (That makes me wary.)
I would prefer a mechanism without such a centralization of moral authority (ex, Kickstarter rather than taxes). That's the big conflict in free societies: the cohabitation of different moralities. (What is a benefit and what is an externality are decided individually rather than by decree or in the average. I think our desire to average things leads us to think we can work backwards from an average to collective behaviour in cases like these, when not everything is a bijection...)
I would prefer a mechanism without such a centralization of moral authority (ex, Kickstarter rather than taxes). That's the big conflict in free societies: the cohabitation of different moralities. (What is a benefit and what is an externality are decided individually rather than by decree or in the average. I think our desire to average things leads us to think we can work backwards from an average to collective behaviour in cases like these, when not everything is a bijection...)