So tell me why should we tell planets such as Volus, or any other planet with a monarch that they can not decide for themselves how their own local government is run?

Monarchy devalues a parliamentary system
Monarchical prerogative powers can be used to circumvent normal democratic process with no accountability, and such processes are more desirable than not for any given world-state.

Monarchy is ethnic-discrimination
By virtue of their narrow breeding mechanisms, most monarchs belong to a clearly identifiable ethnic group. Thus, members of other ethnic groups are forever denied a head of state they can directly relate to. This phenomenon produces divided societies where one ethnic group can, openly or discreetly, boast about their ethnic link to the royal family and derive from it a sense of superiority. In ethnically homogeneous countries, this has little effect. However in multi-ethnic worlds, this can be become extremely divisive and the historical record of constitutional monarchy ability to maintain planetary unity, in the face of multi-ethnic tensions, is not good.

Monarchy is gender-discriminative
Many royal houses uses male primogeniture, which means that the crown is inherited by the eldest son, and is only passed on to a daughter if the monarch has no sons. If absolute primogeniture were used instead of male primogeniture, the crown would be passed on to the eldest child irrespective of sex so that daughters had the same rights as sons. The current method of succession disinherits not only daughters but their descendants. However this is not an argument against Monarchy per se, only against particular monarchical systems.

A monarchy demands deference
It is argued by republicans that the way citizens are expected to address members, however junior, of the royal family is part of an attempt to keep subjects 'in their place'.

It is the enemy of merit and aspiration
The order of succession in a monarchy specifies a person who will become head of state, regardless of qualifications. The highest titular office in the land is not open to "free and fair competition". Although monarchists argue that the position of civil governor or other non monarchical officials, the titles with greater real power, is something anyone can aspire to become, the executive and symbolically powerful position of Monarch is not.

It devalues intellect and achievement
Members of a royal family bolster their position with unearned symbols of achievement. Royals are often fast tracked to senior civil service or military positions... Even unintentionally, due to popular reverence for ridiculous and outmoded traditions.

It harms the monarchs themselves
A hereditary system condemns each heir to the throne to an abnormal childhood. Many are forced to only breed with a select group of relatives leading to inbreeding in many cases. Equally, every royal suffers to some degree or another from long term psychological harm due to abnormally large responsibilities.

Monarchs are not impartial, and lack accountability
Monarchs are not impartial but harbour their own opinions, motives, and wish to protect their interests. Monarchs are not accountable to the people in elections. As an example, the former Queen of Naboo has spoken and acted in ways that have widely been interpreted as taking a political stance, citing her refusal to comply with the Empires Order 66.

I see a lack of important democratic accountability and transparency for such institutions, if a family are a drain on the planetary treasury then they should submit to popular accountability.

Monarchy is expensive
The total costs to taxpayers including hidden elements (e.g., the Royal Protection security) of the average galactic monarchy are over 100 million per annum.

Monarchy makes the a world appear 'backwards'
I argue that the monarchy may be considered embarrassing: as a concept it is archaic, and while a world has a monarchical head of state it cannot claim to be a modern and progressive one. Any world which is not as modern and progressive a world as it can be is fails the Empire in it's basic duties to it's people.

If my father did something of ill repute, a special group of nobles on Anobis were allowed to dethrone him, and have a vote to see who was capable to be the next king.

The king is not always blood. For instance. I can chose to, I could reject my future as King of Anobis, and have the assembly find some one better suited to it.

Perhaps you would consider adding this to your proposal? have what we call an Assembly, on the planets with as you say. "Monarchs" If they are found taking bribes, then it's easily remedied, add an outsider, one from the empire.

This demonstrates the problem, from whence comes the constitutional justification for this coup?

I won't comment on your specific case Senator Fabio, nor do I question that your King is a good man. However the system itself is a bad one. To elevate a hereditary monarch to power sets him above the people, relegating them to being nothing better than slaves.

Needless to say I cannot consent to your amendment as it is not in a legislative format.