Immigrants do not put a strain on public services because they contribute tax money as well as receiving tax benefits. As the number of people grows, the tax revenue grows. Many immigrants are net contributors to the economy because, having moved in adulthood, they have not used costly educational services.
Studies have found that immigrants are less likely to use welfare benefits than native citizens.
Immigrants are a boon to infrastructure because they contribute to the skills gap by providing doctors, nurses, and other needed professionals, of which we do not have enough. Unscrupulous politicians who underfund public infrastructure frequently and unfairly lay the blame on immigrants. Poor public services are caused by persistent neglect and refusal to pay for them with higher taxes.
Immigration does not necessarily cause overcrowding; it's poor planning and a lack of funding that contributes to overcrowding. Immigration allows in people who can be net contributors to the economy and provide much-needed skills.