There's undeniably some truth to that, but your claim about it being a 95% decline isn't supported by that link, and is completely refuted by the current data. http://monarchwatch.org/blog/uploads/2016/02/monarch-population-figure-monarchwatch-2016.png

As the author mentions, year-to-year changes can vary significantly due to factors like the weather, which is why they've provided averages. It's much more accurate to say that monarch populations have declined 43%. Mind you, I'm not saying that that's somehow "acceptable", but at this point herbicide-tolerant crops have essentially reached saturation. If there is further habitat loss, it has to be due to some other factor.

It's also worth pointing out the opposite side of the issue. The adoption of herbicide-tolerant crops has reduced the use of tilling as a weed-control method. That, in turn, reduces erosion which can be extremely harmful to the environment.