I don't think it's a big deal.
Wow, can you explain why you don't think it is a big deal?
It's something people do every day, so I don't really see the problem.
It's good that you can discern small problems from large ones, but keep in mind that not everybody views their problems through the same lens as you. What might seem like a small problem to you may seem like a large issue to somebody else, so it's good to be considerate when someone is stressed about something that seems insignificant. If you tell someone that their problems aren't a big deal, then you may make them feel bad or even angry with you.
I have a right to have an opinion.
You're right, but your opinion is telling other people that something isn't a big deal which minimizes your opinion. While you should never make a big deal out of small problems, to them it might be a big one.