Why don't you use the opportunity to address the points intellectually rather than silently thinking they are wrong?
First of all, the statements are very different. One of your acquaintences advocated prohibition, while the other merely opined that the overall results were negative without supporting prohibition.
What are the dangers in each position? How do the arguments apply to other questions, like voting age? How do the arguments apply to other groups, like citizens/noncitizens or felons/nonfelons?
I'm not an expert here, but I know there are some tough questions here that you might find difficult to answer. And then you might better understand how someone might hold a misguided position.
Really, most peoples' thinking is muddled on these issues because they haven't studied them. The only thing that keeps most people from saying such things is politocal correctness.
Careful here. This can be said about the other side as well to parrot news stations, media outlets and propaganda. This is surely no way to address such a situation - it is one-sided and judgmental. You need to open-minded if you want to hold such a difficult conversation.
Basically I just believe the modern liberal ideas because they sound right to me and I haven't heard any serious rebuttal. "Parroting" might be a bit harsh, but only a bit.
As an individual you may not hold this belief in your heart, you may feel that some types of people are more or less qualified for certain tasks but when you start having a political discussion it is pragmatic for all parties to accept the previously mentioned axiom.
Some individuals are so firm in their beliefs that they refuse to accept the 'politically correct' viewpoint and so they devolve the discussion with arguments based on assumptions that make discrimination a foregone conclusion. Thankfully most people differ in the way they are politically incorrect so they feel that other peoples discriminatory assumptions are faulty, however, echo chambers...