They also decrease the incentive for people to do research and development (e.g: as derivative works from existing inventions).

Which effect is stronger? It is very plausible that overall, the decrease is far stronger than the increase, as the vast majority of inventions are derivative.

What you say may be true in some cases but I personally think twice or three times about doing any hard research and development because the chances are either some megacorp or patent troll will eventually come eat my lunch with bogus claims of infringement and the associated high cost of litigation.

Problem is that patents are not used the way they were intended to. A patent was supposed to be licensable so that other companies could still use the said technology if they so wished. But in practice what patents do is lock the market and prevent the exploitation of said technologies until they expire, which in turn slow down innovation significantly.

And don't even get me started on all the "obvious" patents out there, or the one that clearly are no invention because prior art actually exists - but then they take years to be invalidated, if ever. It is just an enormous debt on Society as a whole.

That may be true, but the current setup in the US at least cost us 500 billion over a decade in litigation alone. Something in our system has to be reworked to minimize the social cost of innovation.