Contrary to popular belief, you can't just disagree with someone because you feel like it. Disagreement is not a fundamental human right (although it certainly seems to be a fundamental human condition) you have to earn the right to disagree with someone's position.
How do you earn the right to disagree?
In "How to Read a Book" Mortimer Adler and Charles Van Doren share a great algorithm of thought to figure out whether you're allowed to disagree with a position a or not and what exactly your disagreement is.
The first step of course is understanding the argument being made, and understanding it deeply. Once you've done that, there are three (~four) reasons to disagree with a position.
If you can't fit your disagreement in one of these slots you are not allowed to disagree. It's rather simple, really.
@cortexfutura
Question to ask (and answer) in order to earn the right to disagree:
Missing information?
Wrong information?
Reasoning Errors?
Non Sequitur?
Inconsistency?
Incomplete Analysis?