Is it worth participating in demonstrations against a system or a person in a country where there is no sense of democracy?

In general, i think that if the majority of society are not satisfy with the situation, it is their right to express their request and unfortunately, most of the time you should say your request in loud voice. More over, the type of government doesn't affect on taking participate in demonstration. However, mostly when there is no sense of democracy the general condition is intolerable and necessity of demonstration is remarkable.

On the other hand, demonstration against one system or person, for another system or person who has no advantage in compare with first one is worthless! and participating in such strike will be kind of stupidity. So, you should know what you want, and you should consider the consequences of your petition.
On the whole, right is achievable. without considering who might be annoyed, you should fight for you ambitions.