Because these two sentences are obviously designed to draw a parallel, look at it point by point.
|People||criminal and terrorists||a 92 year old senior|
|Action||buy an assault rifle||trying to vote|
|Justification||it is an infringement on their constitutional rights||is a threat to our democracy and could destroy our free election system|
Ignore for a moment the ignorance about guns (an “assault rifle” is a very well defined category, which is very tightly regulated in the US). Notice that it is criminals and terrorists who want to buy weapons (as opposed to law abiding citizens, who might have a legitimate need). But the person voting without an ID is an innocent poor 92 year old senior. Also, his or her action is a lot weaker. Merely “trying”.
The assumption, which the meme author would like us to leave unexamined, is that the evil people who form a genuine threat buy guns. The people who want to vote are all innocents who just happen not to have an ID.