In cosmology it would be unfair and perhaps even incautious to ignore the dissent, especially when it comes from highly qualified personalities. The most legendary among them is with no doubt Halton C. Arp, criticizer of the standard model since years and dissent's hero.
Arp's main field is galaxy imaging. Arp has worked at Mt. Wilson and Palomar with the largest world's telescopes and he has been hunting for galaxies showing remarkable anomalies.
For his work he has even been awarded with the Helen Warner Prize by the American Astronomical Society.
Arp has compiled the Atlas of Peculiar Galaxies which includes 388 galaxies with notable anomalies. Nobody argues about his professional skills but only a few astronomers accept his conclusions.
According to Arp, quasars show a clear tendency to cluster around galaxies which should be much closer and that have anyway a much smaller redshift.
One of the proposed explanations is that quasars are all but far and they are, on the contrary, much smaller and closer than it is commonly believed.
If we neverthelss accept the relation between redshift amd recession velocity, this would imply that those quasars which lie between us and the galaxy should recede faster than the galaxy itself, and therefore they should move towards it.
On the other hand, those which lie on the other side should go away from the galaxy, a conclusion which is unacceptable because it correlates quasar's velocity with an accidental alignement between the galaxy and the Sun.
According to Arp, the redshift is not linked with the recession velocity only, but another factor exists, yet unknown, which can alter it. If this is the case, the basis of the Hubble law and almost all cosmology based on the standard model would be deeply questioned.
The reaction of the majority of cosmologists is skepticism.
Arp's criticizers emphasize the discovery of quasars whose distance must be very large because they are associated with small luminosity galaxy clusters and not only because they have large redshifts. Though, the mistery of quasars clustering around anomalous galaxies still remains.
According to others, the statistical analysis of such correlations has some weak points and it should be carefully re-examined.
[...]
Frankly speaking, I think that rancourous polemics are useless and, at the end, facts is what counts. If there is something right in what Arp, Hoyle and others say, given the enormous technical progress undergone by the instrumentation during the past years, astronomers will soon encounter unexplainable objects, whose structure will not give rise to any doubts.

Tullio Regge, "The Endless Universe", Oscar Saggi Mondadori, 1999, p.130-131