The comparison is unreasonable as the circumstances surrounding the two are very different.
The guys are not applying apply the same logic to everything, they are looking at every case separately.
I guess the point of his comparison, albeit poor, which I kind of agree with (but not how he puts it): is to say that just because some person has some strong desire, does not mean it should be carried out...
Lets consider this:
1. The fulfilment of desire, especially by hedonists/humanists, tends to be seen as good as a goal. i.e. the phrase "get what you want"
2. Some then continue to argue, that it is kind of irrelevant how it happens (although this is not what is happening here), kind of like "ends justify the means".
This thinking of "ends justify the means" is what pops up in both these issues, both have "noble" ends, represented by their slogans (depending on how you perceive each issue), the former is """marriage equality""" and the second is """dying with dignity""". Obviously on both these issues, I don't think these ends cut it. With the first, I don't think it is achieved/achievable** or possibly paradoxical*, and the second is definitely paradoxical. Obviously most people look at each individually, by looking at the means, but by picking what is similarly held.
(Note most people think that equality & dignity are good things hence...)
I don't think that DrSoccerball is picking apart anyone's logic really well. (Mainly because his questions need to be reiterated/rephrased to make sense for most). While it is true that each case is unique and different, their is still an underpinning framework...
(*unless you redefine the terms differently, which is what most people do; **by factoring in the disparities)