This is a good question and a complex topic. I'll refer to a wildfire as a fire which causes or conditions were not affected by humans.
Wildfires are devastating events - they destroy big areas, remove/damage vegetation, threat animals and change physical conditions in the fire region. However, on a bigger scale wildfires are part of the natural cycles - they play role in big scale vegetation succession, age structure, nutrients balance etc. So, natural or 'wild' fires are necessary part of a health ecosystem and thus they do support biodiversity.
The problem here is that there are not much 'wild' fires left. Humans are the #1 cause of the fire nowadays. In some regions this increases the frequency of fires and this often has a harmful effect on the natural cycles. (e.g. instead of 10 ha of forest being burned in a time period in a n area, 500 now will be burn) From the other hand, in many regions with high development density wild fires are 'under control'. Historically we as humans try to 'protect' our property and the land from fires. So in some regions preventive measures succeed in making fires a rarer event. This is true for CA. As it turns out, rarer does not mean better. As there is now longer time periods between fires - more dry wood is accumulated in the ecosystem as a fuel. So when the fire finally starts - we have much more severe and larger scale event. E.g. instead of 10 small fires few ha each, we now have a huge one, burning hundreds ha with higher temperature. Big scale and high temperature fires have a bigger impact on the biomes and they may affect the natural capacity of the biome to self-restore after the fire.
The most frontier land/conservation management strategies today include fires as a normal component. However, we basically don't know how much fire is good for the particular ecosystem and thus the 'adaptive management' strategy is used. A fire regime is introduced to the system with known parameters area, temperature, frequency. Than managers monitor how the system behaves and adapt fire strategies when necessary.
In summary, wildfires are indeed a part of natural cycles. Due to human activity, patterns of natural fires, their frequency, their scale and their chemistry change. These changes may have a harmful effect on the ecosystem. We are still in process of understanding the complex mechanism of fire regimes effects on ecosystems.