I don't know if one anecdotal tale is evidence that legalization was a mistake. At most, you've described a case of an inconsiderate neighbor. A neighbor who could be asked if he or she could possibly smoke elsewhere. 

It is an obnoxious smell, and I smoke outside and occasionally wonder just how much the neighbors can smell, and hope that they'll let me know if it's an issue, so that I can try and find somewhere else to do it, or to try to smoke when they aren't home. I already do this as much as possible, weather permitting.

Something being an inconvenience to someone, however, isn't really reason to make it illegal. I haven't seen any studies indicating that incidental secondhand cannabis smoke is all that hazardous. By the time it's wafting into someone else's house, it's dissipated greatly from the concentrations that the user is inhaling.