I remember being really young and believing immigrants were a good thing. The need "skilled workers" and "do jobs Canadians won't do" narratives work which is why they keep using them. Most people are raised to believe all humans are equal but have different upbringings so immigrants should be given a chance because once integrated they'll be just like us. Also, most people think there's some decent minimum standards for immigration. Then people think we take in so few refugees that we should be nice because they need help and we're a wealthy first world country that can afford to help them. Finally, people think the temporary foreign workers are truly needed for the industry because why else would we take them in if we didn't need them?
It's just a lot of blind trust of government and the institutions running out society by people who don't know any better. Sadly, because these people side with the institutions, that gives them perceived credibility in being right because they trust the institutions. They believe anything who says differently must be a moron because they're taking an opinion not supported by the majority of people and they believe the majority of people are trustworthy, knowledgeable and working toward the good of society.
These Reddit people are hopeless but if we did take back control of the institutions, they'd eventually switch all their views in time.