Why would microeconomics be considered more "objective" than macroeconomics? I can imagine the following reasons for this: 


conflation of positive vs normative economics in macro
micro phenomenon is less complex (or smaller): thus easier to create reliable models for


Thanks
I used to think that microeconomics was relatively more scientific than macroeconomics. Early macroeconomics, in particular, suffered from choosing models of agent behavior that made modeling easier but bore little relationship (or at least a highly disputed relationship) with reasonable behavior of individual agents. This led to the microfoundations effort, which attempted build macroeconomic models from the ground up by modeling the behaviors of the economic agents in line with microeconomic theory (rational expectations, utility functions, life cycle effects, market power, and so on). Aligning macroeconomics with microeconomics strongly implies that microeconomics &quot;has it right&quot; and macroeconomics does not.
However, that's not the end of the story.  In a nice essay called The Macroeconomic Foundations of Microeconomics, macroeconomist Mark Thoma says that microeconomics has a lot of hidden macroeconomics lurking in the background, and it is important to recognize this and formalize the role of macroeconomics in microeconomic theory. For example:

One of the lessons from macroeconomics is that prices do not always
move fast enough to keep markets in balance, and this observation --
this macroeconomic foundation -- needs to guide microeconomic
theorists. The Walrasian auctioneer is a convenient theoretical
assumption, somehow prices always magically move immediately to clear
all markets and attain the highest possible societal welfare (and it's
useful for comparing long-run outcomes). But that assumption is not
very useful as a foundation for macroeconomic models that try to
explain short-run swings in the macroeconomy. Microeconomic and
macroeconomic models ought to be consistent with each other, but the
microeconomic foundations need to have realistic assumptions about the
ability of price changes to clear markets.

More generally, microeconomics usually assumes that microeconomic agents are embedded in a functioning macroeconomy. An economy with functioning markets for other goods, property rights, production functions and industrial organization that makes supply curves, demand curves that are well defined, and the like. This joint dependence on the assumptions of the other family makes the two major schools of economic thought closer to peers than the microfoundation revolution suggests.
That said, microeconomics has done a lot more to bring experimentation (field and laboratory) into their research. This has helped inform their modeling and econometric work in a positive way, including this year (2019's) Nobel winners. For ethical and financial reasons it is much harder to do this in macroeconomics. This could be a reason to think that, in general, microeconomics might be a bit more objective. However, the majority of microeconomic research is non-experimental, so we shouldn't go too far with this argument.
I also recommend Raj Chetty's essay Yes, Economics Is a Science for a comparison of the scientific bona fides of the field of economics with other scientific endeavors, particularly medicine.

It is true that the answers to many “big picture” macroeconomic
questions — like the causes of recessions or the determinants of
growth — remain elusive. But in this respect, the challenges faced by
economists are no different from those encountered in medicine and
public health. Health researchers have worked for more than a century
to understand the “big picture” questions of how diet and lifestyle
affect health and aging, yet they still do not have a full scientific
understanding of these connections. Some studies tell us to consume
more coffee, wine and chocolate; others recommend the opposite. But
few people would argue that medicine should not be approached as a
science or that doctors should not make decisions based on the best
available evidence.
... Nonetheless, economists have recently begun to
overcome these challenges by developing tools that approximate
scientific experiments to obtain compelling answers to specific policy
questions. In previous decades the most prominent economists were
typically theorists like Paul Krugman and Janet L. Yellen, whose
models continue to guide economic thinking. Today, the most prominent
economists are often empiricists like David Card of the University of
California, Berkeley, and Esther Duflo of the Massachusetts Institute
of Technology, who focus on testing old theories and formulating new
ones that fit the evidence.
This kind of empirical work in economics might be compared to the
“micro” advances in medicine (like research on therapies for heart
disease) that have contributed enormously to increasing longevity and
quality of life, even as the “macro” questions of the determinants of
health remain contested.